Zo, my understanding the 3rd party stuff is not there yet, at least I can't get it to work. I have not been to the NI forums for a few days so not sure if anything has changed yet. Now, if you mean 3rd party Kontakt libs that will work now.
You are right that you do still need the computer screen to really see what you are doing but I can't imagine the small screen on the Akai being much better for my old eyes...
My main attraction to the S61 is the Touch Strips. Undoubtedly the best dynamic vibrato I've ever been able to get using the pitch bend strip to create a Real dynamic vibrato just by rolling my finger back and forth on it. Most other pitch bend controls, i.e. wheels, joysticks, etc. have a dead band that makes this technique impossible for me. YMMV.
If you have a chance you should try them both out before making a decision. I would imagine that NI is under the gun to get the 3rd party integration out before the release of the Akai but who knows...
edit: After reading Larrys' post I remembered that you do have to map the 3rd party Kontakt Libs yourself and add your own icons. Not a big deal as you only need to do it once and save it.