Okay, I haven't touched 9 yet or really followed the development closely so I'll be brief.
- I doubt UFS will be abandoned in favor of ZFS any time soon. If it was, the devs wouldn't still be working on improvements and extensions from time to time (including now -- 64-bit quotas). ZFS may be the default (i.e. not only) FS in the final RELEASE though.
- The entire installation program is new and intended to replace sysinstall completely. As far as I know there was UFS-only support when they started and people were complaining and "getting desperate". The devs have probably added ZFS support not so long ago and are testing it.
- This is a CURRENT (development) snapshot and we're 2 months from the expected RELEASE (definitely more from the "real" one). Give them some time. If you encounter problems while testing, submit a PR if no one else already did.