What's the problem? Give them the same body types, fix the bugs for gear, make them like Twi'leks and remove the helmets and hoods if problems persist. And how many voice actors do you need to make a Wookiee say OOOORRAAAAWR?
Same with Trandoshans. We can make Trandoshan and Wookiee NPCs, give them subtitles, then tell the playerbase it can't happen because of facial experessions? Shenanigans, I say.
I don't think people would buy them taking human bodies, making them hairy with Wookiee heads, and calling them Wookiees. Their signature body types are just too different to pull it off without a TON of complaints. It would be uncanny and weird to have short, broad-shouldered Wookiees running around, and I think trying to pull off a female wookiee with the existing female body types would be even weirder.
So let's pretend they DID release wookiees at their correct size:
--Speeders would have to be resized or restructured. (Non-human companions are the reason why they scrapped having your companion in your speeder at the start.)
--Cameras would be off in cutscenes. The (cutscene shots are composed with the 4 body types in mind, so a lot of restructuring would probably have to happen).
--MANY more animation combinations (I remember reading about how each melee move varies by which body type is fighting which, which multiplies each of those ability variations significantly when you add in a new one.)
--Major gear reworking (don't think I have to mention this one). Actually, one workaround for the gear thing would be to allow players to just not wear gear and purchase customizations instead (like the ones for Bowdaar). But being able to change your character's look one gear piece at a time is a major hook in MMO's and going around with the same "kits" as others would probably make a lot of people lose enthusiasm.
Regarding voice, there would have to be a TON of variations of their speech or people playing one would notice all the repeats, and those repeats wouldn't be corresponding to the right meaning.
Also, we'd have to break lore with the whole language thing. Should we assume all NPC's know Shyriiwook? Do they all have translators? Sure, we already know lore isn't sacred in this game with legacy and such, but still, it's a big stretch.
While it wouldn't be "physically impossible" to introduce this species, I find it very, VERY unlikely...