ZFS Native File system
Native NTFS write capabilities
Better/Faster Open GL support
Trim support for SSDs
Better/Faster HD Video Decoding
I really believe that 10.7 will be the last OSX... there really isnt much more to work on or add or perfect on.
I think that OS 11 will be a OSX + iPhone OS Hybrid, and that will debut after 10.7
ZFS is probably never coming back to Apple again. The Oracle's acquirement of Suns changed everything. It is more likely Apple will use BTRFS instead of ZFS or they'll work on their own next gen HFS. I don't think we'll see anything regarding to a new file system in 10.7, since BTRFS is still an immature FS and Apple started hiring new file systems engineers after dropping ZFS which suggest we're years away.
Trim is likely to come with the new file system but regarding to 10.7, i think we might see some kind of an enhancement to the old HFS+ but they could've done that for 10.6. No news to report on this.
Native NTFS write support is already in SL, you just need to enable it by mounting it with an RW option via command line. I think I saw some tool that can do this for you, check google for it. I think Apple will enable it by default in 10.7 once the driver continues to mature.
Better/faster
OpenGL is coming already via 10.6.x updates, 10.7 will just continue the pace regardless.
Better/Faster
HD decoding is a definite. 10.7 will continue the optimization and maturing of the OpenCL, likely to have OpenCL 2.0 release support.
There won't be any Mac OS X + iPhone OS
hybrid, because there's nothing to mix with. iPhone OS is nearly the same thing as OS X with its front end being tuned for the touch screens and Mac OS X is tuned for the desktop use. If Apple releases iMac/Cinema with touchscreen support, then the interface will be tuned for it, not likely to be the same as iPhone's interface, it'll have many of its graphics but the way we interact will be different.
Steve Job also said and I'm paraphrasing, that 10.6 was built to build the next decade worth of OS X releases. That was the whole point of 10.6, to modernize the cores so that they can get the OS up to date and ready for new technologies and innovations in the next several releases.
With all the new foundations, I don't think Apple is going to radically change to something else right after 10.7, it's too soon. Apple has the OS that they're ready to work with. With no more PPC code in it and likely the 32bit CPUs support bring dropped for 10.7, Apple finally has a near clean codebase to work off with no worry about PPC/32bit support.
Apple could easily rename 10.7 to OS XI if they want to, especially if it'll continue a brand new file system, brand new interface and so on. The question is, can they get those done in time? Probably not, could they get it done for 10.8? We have no idea.
I honestly think 10.6/10.7 combined itself would've been OS XI.