As far as I understand what's been written on the Riker9 threads, the framerate will rise as far as your system allows it. The game itself will not be faster, but a lot more smooth to the eyes of the player.
Depending on what Cellbloc is doing, you may have improvements on what you can do without loosing what you are able to do right now, meaning: your maps will work fine and depending on what's offered you will be able to do more. We will have to wait and see though.
One very important thing is the ability to save and load, as far as I'm concerned the biggest flaw in the actual build and that will be dealt with if I'm not mistaken.
If you ask me, Riker9 is a major improvement on the actual engine build with FPS resolution and save/load feature. But if I read Cellbloc's acknoledgments correctly, more was done to improve, like getting the culling problems solved (slap my wrist if I'm lying Cell
)
If you are making your levels and are comitted to do it, you should not stop because of this project though. Even if there are major changes whatever you'll learn with the actual V1 will prove very useful in getting better levels and games when Riker9 is out.
Good Luck.
I'm pretty sure I know everything. Doubts are something rare in me and I am never wrong, as this signature can prove.