I expect to see a leaner, faster, more stable OS that simply works better and meets the needs of 'most' users. There will be some who complain about this, that and/or everything about Win 9, but that is to be expected when some aren't happy unless they're complaining.
Thing is, the orgins of Win 9 are based in Win 8, and any under the hood improvements that get raved about will the consquence of Win 8 being such a good OS... under the hood. Sadly, most people saw Metro as being THE face/UI of Win 8 and didn't really look too much further to see just how good it was underneath. Oh well, I didn't miss out on the performance boost and improved speed of Win 8, cos I liked it from word go and have used it as my primary/only OS on my main rig ever since.
As for Win 9, I'd like to see Metro and the Store as options that can be accessed from a desktop icon, even pinned to the taskbar, perhaps, then users who find various apps useful or productive can access them without losing their desktop or have to go through a performance to get to it. I do like to browse the store for new apps, and I have some that I use regularly, so have my start button bring up the regular start panel as needed, but I use the Win key to bring up Metro as needed, and I find this efficient as well as non-intrusive as far as Metro goes. Perhaps this could be a feature of Win 9... for those who want it, Metro, that is.
Another thing I'd like to see in Win 9 is a faster copy/move ability. Yes, USB3 and SATA3 provide greater speed but Windows hasn't really kept up with that IMHO. It is better in Win 8 than in previous iterations, but even so there are faster file transfer programs out there, like TeraCopy, for example. However, a faster copy/move function natively would be a welcome addition to Win 9.
I saw in an earlier post that Libraries were not a desired feature and if fact are annoying. I too would like to add my voice to that. I do not like the Libraries function, either. I know where I put my files so don't need an addition that can get in the damned way. So for mine, make it an optional feature users can select at setup if desired. Otherwise, get rid of it.