I would urge you to reconsider this. A lot of people don't actually care about the dialogue, and just want to play something interesting and unique. Certain mechanics will affect everyone, but a playable species that makes a portion of the population very happy, and doesn't interest the rest could still work. The only real question is just how many players would be interested in a species that can't speak basic, I can't answer that. I know some players hear about a near human species, and instantly stop caring. I know a lot of players that would have mad respect for this game for doing some less likely species.
I only ask that you consider that not everyone is going to have a strong negative reaction to this prospect.
I am with Rylorn here. Afterall, if we can sit patiently through Blizz babbling through a bajillion companion conversations, a few 'Oota Goota's' from a Rodian or growls from a Wookie PC (these are examples), aren't going to kill us.