TFS was created to speed up the development. The issue is that following the design specs makes it much slower to implement, and prevents a "natural" development (like, you cannot implement it like a tower, you need every component before completion). It was started[1] and got far enough to reading images, but implementing it took ages, so we decided to put it off for now.
This doesn't quite seem to follow? ZFS's pool model has supported flagged off features for a very long time - isn't the issue more that to do the things ZFS does you need to implement all the other components? And since you're planning to do a lot of what ZFS does...
