Aside from cost there are far more factors *against* voice acting, such as having to lock content at some point to have a clear copy to the actors, and then not being able to change it anymore.
Heck, the EE would have been hell if the whole game was voiceacted since all the added stuff, changed stuff would have required a full re-voicing, and if the actors weren't available they need to re-voice *everything* for that character. Compare them with just adding more branches now.
Also Larian was basically adding and writing to the game till release with D:OS. Due to the lock that I mentioned before Larian wouldn't be able to do that this time around, if they went with full voice-acting.
More negative sides of full VO is that mods will stick out even more since they will need to do equal voiced characters or stick out as a sore thumb. And getting VO for a mod is NOT easy, take my word on that (and if you won't just google 'my' mod "M4-78EP").
Also funny you mention BioWare since I'm pretty sure it hugely bit them in the back with The Old Republic (100+ million dollar budget IIRC, and that was even with a lot of alien VO surplacing human VO).
So in conclusion I can only say "no, no, no, no"
Just compare the amount of text in, say, Pillars of Eternity (not full VO, even if they voiced too much *everyone agrees!!!*) to a BioWarian game. That's like comparing the Lord of the Rings trilogy with a 150 page teenage romp. And then claiming it 'improved'...
