I start by stating a problem with alchemy, or a set or problems that I think needs to be looked at.
First, it is insanely tedious.
The duration is short to prevent abuse but the result is that the mage needs to remake all preparations every time and plan her sleep in detail to get maybe 2-3 possible preparations for a run. This leads to a LOT of dice rolling for things that are rarely used and it bores every other player to wait.
1 Mage rolls Alchemy
2 GM rolls Force to "resist"
3 Mage rolls drain resist
4 Mage notes Potency and starts boring timer to tick down the duration
5 Mage rolls stun recovery
This is almost if not as boring as Widget submersion technomancers that rolled threading, widgetcrafting, multiple fading resists on top of the already super long extended tests that littered SR4 matrix that we thankfully are rid of now!
Second, it has extremely varied utility, typically bad.
Any spells that offers a resistance test end up being outright pathetic.
A mage with 18 dice Alchemy making a Confusion illusion will still end up with a thing that has some 8-9 dice to cast the spell (F6 + maybe 3 potency), versus 15 dice object resistance (to confuse tech) that isn't exactly useful against a nonliving target. Even against a relatively helpless super dumb troll (Intuition 2 and Logic 2) he is looking at a 1-2 dice pool modifier while any meaningful target will at worst get a -1 penalty...
Players need to have the statistical knowledge to realize this and only pick spells that work with low dice pools. Levitate, Heal, Increase Attribute are good examples, the rest is terrible.
Third, the mage needs the spell as preparation too
A 5 karma tax is applied to even know the spell as preparation in the first place. A mage picking Alchemy will probably have 1-2 spells as preparations in total so it is extremely limited.
Fourth, it is a very weak mage mechanic
I know mages are powerful and needs "nerfs" but to make a crappy tool even worse is hardly helping. It only puts even more focus on the problematic tools of Mob Mind, AoE indirects instakill and classic spirit abuse. Making more of the mage tools useable draws attention (and karma/skillpoints/etc) away from the overpowered stuff and gives room for serious mage players to create fun and useful characters without making their team obsolete.
As it stands now, people hate mages because all every single mage does is toss instagib-aoe lightning around while having 31+ initative on every round, not because they have a big toolbox of utility or provide cover from other mages to the team. (Counterspelling nerf from previous edition only makes mages even more annoying)
So, yes, I want to make alchemy usable and fun without breaking it.
What to consider when "fixing"
Some mechanic needs to be there to discourage mass-production of preparations that doesn't involve tedious bookkeeping (per hour decay bs) or break tempo (+2 drain is a poor way to reduce the production of preparations, all it does is make several rounds of spellcasting, resisting and resting just before a run).
We need to focus on what role we want Alchemy to hold and what to keep
1. Action budget, using contact preparations to cast more than 2 spells per action phase (or some reading rules backwards allowing command to break action budget rule too)
2. Drain budget, casting spells without drain in combat is worth the "penalty" to dice pools alchemy have in practice for some spells.
3. Avoiding sustaining penalties. Sustaining spells is a nightmare since Sr4, especially since it says "all tests", including damage resists if you read the stupid text. However, the INSANE buff to Quickening in SR5 makes this point rather empty.
4. Creating "mines", variation of point 1, but a contact fireball or illusion sounds fun.
5. Avoid wound penalties, casting at full Force+Potency might be higher than Magic+Spellcasting-Wounds-Stun-other debuffs
Regarding (1) I personally see no reason whatsoever to break action budget rules. One attack per phase is a really good rule that severely limits characters ability to kill all enemies the first action phase of each combat. SR4 dual wield with split pool attacks let you murder 4 enemies per round and still have twice the attack pool as the enemy defences... No, action budget breaking is not a good quality for Alchemy!
(2) I see a point in drain budget, having some backups when drain (or stun damage) is making regular casting impractical. So, ok for this
(3) Similar thoughts goes for sustaining avoidance. A time limited selfbuff that doesn't make you handicapped opens up a LOT of buffs for usability. Current system makes many of the buffs very limited. Who wants to take -2 to everything for +2 armor? It cancels out for damage resist and is a net loss for everything else. You need to score tons of hits on the initial cast to make it even marginally useful. The normal way to avoid this is to use sustaining foci, focused concentration, buffspirits or quickening metamagic. The alchemy way of doing this is less cheesy than buffspirits and quickening so I think this is good.
(4) Forcing creativity out of a mage is a good thing. Needs caution to avoid breaking (1) though. Making all pellets in a shotgun a Fireball preparation and then fire at someone is not acceptable.
(5) Fine
If you have read this far I applaud you!
My attempt at new Alchemy:
Preparations always cost Force reagents and preparations are always full Magic force. Creating a preparation takes hours but the result lasts "forever". A maximum of Alchemy skill number can be made at a time and they need to be stored for longer times in the mage's lodge.
Potency is the hits on the alchemy test, no extra resist, Limit on the alchemy test is the lower of Alchemy and Force, since preparations can be made days in advance drain is usually not an issue and doesn't need to be rolled.
With drams being used every time it is a money sink for mages, with limit and force fixed it avoids "lol F14 fireball"-crap while still being useful for buffs and debuffs alike. The dice pool of a preparation is generally buffed in this version but I see no trouble with that.
Using a preparation is a simple action but requires the item to be held (normally a simple action to pick up the preparation unless you run around with preparations in your hands instead of a gun or whatever) and follows the one attack per phase rule like everything else. Debuffing spells counts as attacks of course.
Preparations can be known alone, you don't need the spell and the same spell again as preparation (like some might read the current rules).
How about +2 karma for making a spell available as both preparation and regular spell instead of 10 karma for both?
And, as a side note, how about changing Quickening back to how it was in previous edition: Karma cost is equal to the Force of the spell and limits hits to Force no matter what reagent/edge-cheese that was used to cast the spell.
13 Karma (initiation 1) +1 karma and one lucky roll Increased reflexes with edge that gives 14 hits for +4d6 +14 initative permanently is simply retarded.
Same goes for Foci or Focused concentration btw. Max hits to force/rank of focused concentration. My players don't even dare to ask if they can take Focused Concentration 1 and put Force 1 Edged Increase Reflexes in it but I don't want to leave the gaping loop hole even open