The Slot format was created because it wasn't possible to integrate all the cache onto the same die as the CPU, because they couldn't make the cache run at the same speed as the core. Now that they can do that, the Slot isn't needed.
The Socket format (370 or A) wasn't created in order to make up for some lack, so it will be around for a while. However don't expect to keep it as long as you were able to keep a Socket7 board. Only the next few iterations of Intel and AMD processors will work on it, then they'll be moving ahead to more pins.