I think voice chat would be a valuable feature at Ask Ubuntu. Obviously some individuals cannot ask a question correctly when it comes to typing it because I see it said by other users all the time. Maybe if they could just ask the question out loud it would be easier for both parties involved. Also a person wouldn't have to see so many cry about how a question is asked.
Ask Ubuntu is not tech support
Many sites have a live chat option where users can get instant support, from someone paid to provide this service. This isn't always voice chat; it's often text-based (and I prefer that because information written down is easier to copy and refer to, but others will prefer voice chat for various good reasons). What's special is that it's live. Someone has to be on call to provide it.
That's the main issue with your suggestion; nobody gets paid here. I can't imagine anyone wanting to tie themselves to a headset to provide live tech support for free. Of course, we like to help the person who asks. Helping people feels really good. But I think what motivates many people to contribute here, aside from the gameification aspects of the site, is that we are creating something that survives, we are publishing work that helps many people now and in the future, not just one person today.
Ask Ubuntu is not a tech support service:
Ask Ubuntu is a question and answer site for Ubuntu users and developers. It's built and run by you as part of the Stack Exchange network of Q&A sites. With your help, we're working together to build a library of detailed answers to every question about Ubuntu.
Well, maybe a bit...
This said, we do have text-based chat. For example here's the Ask Ubuntu General Room. It's used for socialising, silliness and occasionally site-related discussion. Often, people come in and ask for help and get what I call "tech support". That's not really what the main chat is for imho, and it's nice if long tech support exchanges move to one-on-one chat rooms, or turn into a valuable question on the site, but often, someone in the room with nothing much else to do knows how to help the person who wants help, or anyway has suggestions, and tech support happens. The entire chat history remains available as a "transcript" for anyone who might benefit from reading it in some way.
One of the problems with voice chat that isn't a problem with text chat would be that very often tech support questions require the exchange of information, like log file contents, output of commands, lines of code, which does not lend itself to being spoken. It might be many lines long, or require every character be exactly correct, or have special characters whose names are not standardised... Also, very very often, replies to a question brought up in chat, or part of them, are links to questions on the site (folks have been working on this Q&A library for a while now).
How can we help users who struggle to interact with text?
You're bringing up an accessibility issue and all such issues deserve attention. You talk about users not being able to type their questions well. I'd say 95% of the time issues with the phrasing or formatting of a post can be fixed by editing. When what a user has written is not understandable and so cannot be fixed by editing, the reason is very likely that they don't know English well enough to write it clearly, and/or they used a translation service, and wouldn't be able to speak English either, and so wouldn't benefit from a voice chat, unless they could chat with someone who speaks one of the languages they do know well. I guess the Englishness of SE is its biggest access issue, but at the moment, the only thing I can think of to help this is to write posts in machine-translatable language.
I know well that there are people who know English and could benefit from information here but who can't read or write easily, because I work with people like that. Fortunately, text-to-speech and speech-to-text technology is getting better and more widespread all the time. Writing posts in a way that aids accessibility is important. Including descriptive alt text and writing in clear language helps.