CFast is based on Serial ATA which is not being developed past the current 6Gbit/s. Read for yourself at http://serialata.org http://www.compactflash.org
It's not 16Gbps SATA, it's 16Gbps SATA Express. Which is different. SATA Express is essentially SATA software stack on top of electrical PCI-Express. (So different connector, etc, etc) Would of course be great with a 16Gbit/s SATA Express host that can also take CFast 2.0 cards, but so far there is no evidence that is happening. I have no idea if that's even possible as there are limited number of connector pins one can fit inside a camera. (They make dual host connectors for PCs that can take both types.)
Should also mention that SATA Express is largely viewed as a transitional standard. So far it has rather few takers, and a lot of companies are looking to bypass SATA Express all together and jump to the next thing. So it doesn't appear at this point that SATA Express will gain the widespread adoption and support that SATA has.
So, IMHO CFast 2.0 appears to be the last iteration of that memory card standard. With whatever that means for widespread adoption, residual value and support. If that is not the case, and CFast 3.0 that is backwards compatible with CFast 2.0 cards is in the works, the players who support that should publish a future roadmap ASAP!
There is of course something to be said about what works here and now! Even if it isn't upgradeable in the same way we have become accustomed to with CF cards.
Yes, SATA Express is the follow-on to SATA, and XQD is the follow-on to CFAST.
Successors aren't always backward compatible.