the system would be much more scalable and is much more scalable with *not* using MySQL for storing sessions and RC is performance wise the weakest part of the whole infrastructure
You probably have a different view of what it means to be scalable than the rest of the world. Scalable means you can add more servers to handle the load. Using a ramdisk is about the least scalable thing you can do. It's great for performance, not so great for scalability.
- no session file locking (parallel requests do not wait)
and no integrity and cleanups or how do you explain me the 5000 records in the session table on a server with a few users after some months?
I have no such issues. Our session table looks sane to me. My oldest session entries are 5 days old.
Cor