with my extremely sofisticated and intricate knowledge of advanced mathematics, I'd come up with a little different approach to damage track, so here's the "huge" difference

instead of calculating your number of boxes based on 8+½ body, how about making it 6+body (or if you're an evil GM 4)
This will essentially lower the number of boxes for people with body up to 4 by one, after that you actually benefit from this variant and gaining slightly more boxes based on your body

The following stats will be based on Core, followed by the the variant and the later the evil variant

Body 1: 9, 7, 5
Body 2: 9, 8, 6
Body 3:10,9,7
Body 4:10,10,8
Body 5: 11,11,9
Body 6: 11,12,10
Body 7: 12,13,11
Body 8: 12,14,12
Body 9: 13,15,13
Body 10: 13,16,14
Body 11: 14,17,15
Body 12: 14,18,16
Body 13: 15,19,17
Body 14: 15,20,18

Let me just throw something out at you, here.

In my group, our Tank Sam(a human, not a troll), has body 5, and 1 full Cyberarm. So, by your chart, would have 12 Health boxes. This character also has 9/9 armour, and a+2 to DRT from Bone Lacing. This yields 16 dice on a soak roll. By the law of averages, this means this character will soak 5 1/3 boxes of damage.

If this same sam were made a Troll, and had a 10 body, with the same gear and cyber, we would be talking 22 soak dice, or 7 1/3 boxes soaked by the law of averages, with 14 standard health boxes, or 17 by your rules.

So, if we applied the laws of averages here, our human can take most light pistols with pretty much impunity and take minimal damage from heavy pistols, ands the troll can take heavy pistols, and can get by with minimal damage from many heavier weapons.

Now, by the book, the human samurai has as much chance of shrugging off small arms hits as from yours. However, when you get to a point where a Troll can reasonable take one extra burst from an assault rifle...or can potentially eat one assault cannon hit(18 dice, or 6 soak, so 4 damage) meaning it would take 4-5 assault CANNON hits to take the troll down under your rules, while under the standard it would take only 3-4. While, at the lower ends, your idea does seem to be good, it breaks down at the higher levels.

And, what does it add to the game? Why do you NEED to increase the survivability of Trolls and Orks that much? Are you finding that they are dying to heavy weapons fire from things like missile launchers and and full auto burts loaded with EX-EX too easily? Is it your players who are doing that to your NPCs? or are your NPCs hosing your players way to easily? Or is it that your weaker Body players are shrugging off hits too easily, and you want to reduce their survivability?

More of making Body a more worthwhile score as practically the only thing you'll ever use it for is three different skills and soaking

wow, beyond my first argument with how SR4 handles body + variable condition monitor, this pushes the players to play troll and orks even more.

That rule sucks mostly, because you weaken avarage people, making a high Body a necessety. I don't think this is a good idea. If you want your Bad Ass plaxers be even more Bad Ass, increase the damage track by 2 or something, but leave the Body/2 part as it is. You will break your game.

Also, if you change the way physical damage tracks works, you should apply the same change to stun damage tracks, otherwise you increase the value of stun spell and weaponry even more.

I don't know if it'll break the game, but penalizing Body < 4 characters even a little seems like a decidedly not-cool thing to me. I know most of my characters shoot for a body of 4 since that lets them wear the 8/6 armored jacket without encumbrance penalties so maybe it doesn't matter that much, but I've seen a number of body 3 characters, too, especially mages/technomancers who need a few extra BP for their Magic/Resonance attribute.

Hm, I guess what sound's good in theory never work in practice

Yup..just ask any engineer or military strategist
Don't get me wrong..it can seem that damage tracks are really short(especially compared to a certain cancer causing game which always had the problem of heroes jumping off a cliff, pulling out their weapon, and wading through hordes), but that is because Shadowrun 4th is meant to be rather lethal combat wise for everyone. I can understand the desire to make them longer. Of course, then again, they ARE longer then the old 9 box track in 1st through 3rd editions, and now, you can survive a hit by some weapons that previously were 1-shot Wonders.(You might WISH you were dead after someone shoots you with an assault cannon, but, chances are, you might survive it)

Now, as for making Body more useful, think about this: Body determines your Damage Code, it determines how much armour you can wear without being encumbered(and, thus, increasing your soak), it is used to resist deseases and toxins, it and armour is used to soak, and, yeah, it has some skills associated with it, too. I am sure there are more uses of Body that I have left out, too.