"Motherfucker looked just like The Thing!"
Exactly.
QUOTE (Karoline)
So, corpses look like they are alive, and joe average can be possessed without any added requirements other than him existing.
It may be in the rules, but I'd veto that in my personal game and I try not to use rules that I'd personally veto when making a character. The body is dead. At best, your regeneration would keep it the way you found it. On the plus side that applies to a homunculus in my book, too, so they wouldn't go sprouting leaves or any of that other silliness. Do metahumans start reverting in age and eventually becoming a fetus? It'd have to in order to stay in theme with that.
I'm also not convinced about your reference to the lack of preparation being needed. Why even mention it if it's not an issue? Why even have rules for it for general possession if it really only applies to inhabitation? It's also incredibly lame because it means that anyone who plays a mundane character can be fucked over at any time by an astral entity on a whim. And, apparently, there's not a damn thing they could do to stop it. It's also contrary to the whole "you can't affect anything on the physical realm if you're on the astral plane" rule.
That said, I think the "may" in your quote is referring to exactly that. You may possess a vessel that hasn't been prepared, but only if it's astrally active so you can jump into it after cleaning out the spirit that was in there one way or another. Mundane vessels still have to be prepared because you have no other way of accessing the body from the astral. The rest of the context of the rules you quoted (and if you could give a page reference when you do that in the future, that'd be great; took me a while to find it) seems to agree with that assessment. Especially the second paragraph where they give an example of a vessel that doesn't need preparation.
QUOTE
And sure, you get a +3 to physical stats, but you have the added limitation of having to stick to your body.
Like you said previously, that's not so much a restriction as an adherence to other character types. And it's only a +3 if you jump into an average human. There's still the plasteel homunculus you referenced, too. At only 15,000¥ at Force 6, that's a whole 3 Karma in the Karma Generation ruleset. Hardly a money sink. It also doesn't cost you any Essence or cause Magic Loss. And they do indeed get +8 to Body, +8 to Strength, and +8/+8 Ballistic/Impact armor. For someone who was so vehemently opposed to cyberlimb armor because it was cheap and didn't impact your encumbrance, it seems a little odd that you're totally okay with that.

And possessing a corpse, no matter how you try to hide the fact, is a recipe for disaster in the hands of any GM worth their salt. An Assessing Test can detect its true nature with a single net hit.