I understand the OPs desire to buy hardware for 8.10. I BELIEVE there will be better support for some things like the Intel Atom boards that right now require a bit of manual intervention. As for a date, I don't think anyone can give you a reasonable answer because nobody knows. Community driven work like this is a "when it's done, it's done" thing, unlike commercial products that have publicly advertised release dates with financial impact when they are delayed. Granted, opensource products often have estimated release dates and people work to try to meet them. In the end, I'd rather have something that is reasonably complete and tested instead of something that was rushed out the door to make the bean counters happy.
What I would do if you really want to get started now is to check out the hardware you want to use with 8.10 then check to see if you can make it work with 7.10. If you can, go ahead and get it and start using it now. If not, hold off for a while or go with something different. Probably not very helpful, but it's the best answer I can give based on what I've read here and the bit of lurking I've done in the dev forum. Speaking of which, it may be worth while to read what's in the dev forum. Just try to keep the user type questions here so the devs can stay focused on what they do best.
Or we may be surprised and a dev may post here that they have a rough idea on a timeline they are shooting for?