So, if it OpenSolaris based, then nothing to see here. Community is too small. Who will write and test up-to-date drivers for all new hardware that vendors are pushing to the market each half-of-year?
Why should that matter for cloud hosting? If you wanted to be able to install OpenSolaris on random hardware it might matter. But this is a closed environment where you never see the underlying hardware.
If it will be a closed platform, it doesn't matter.
I had a lot of experience with Solaris (x86 only - people tried to run Informix/Oracle on a cheap hardware) starting from Solaris 7 and onwards. It was always a problem even to install it. And lack of working compiler makes things even worse.
Starting from Solaris 10 they did a lot of work to improve the overall experience, but too late - everyone migrated to Linux to run the same crap.
And I must say, that after it was installed and tuned it was running quite stable as a database server and it can deal with heavy loads, while similar Linux instances failed now and then. But it was 5 years ago. Modern Linux kernels can handle everything quite well.
Oracle, just like Sun before it. Each time they do a code dump, the new and changed drivers can be integrated into Illumos by Joyent and other companies that depend on Illumos. Sure, it won't support "all the new hardware", but it will support enough. If they decide they need to, Joyent has the resources to do their own driver development.
Tomorrow they (Oracle) will decide to "slash the costs, do restructuring and refocus on their core businesses" as Cisco recently did, and guess what? ^_^
Considering that many of the most talented Solaris hackers have left Oracle and now mostly work at other companies that depend on illumos, I strongly doubt that they can't write their own device drivers.
Joyent probably has fairly homogeneous racks of servers. They only need a few drivers for their entire system, and they have people capable of writing them. If they can port KVM from Linux to illumos, what makes you think they can't port or write a driver?
No, I have no doubts that well-funded commercial enterprise can keep its code up to date, I considered from the Open Source, community-driven point of view.
So, if it OpenSolaris based, then nothing to see here. Community is too small. Who will write and test up-to-date drivers for all new hardware that vendors are pushing to the market each half-of-year?