We'll definitely see support for multiple displays and more RAM. Incidentally, these limitations were also present in the lower wattage CPUs from Intel. We'll see more storage as well, but I imagine few folks looking at the entry-level models need more than 2TB. I doubt we'll see booting X64 OS versions anytime soon, if ever. I also think that there will always be some tasks where other silicon will perform better. This was the case back during PPC vs Intel, and before that when it was 68K vs MIPS vs. PA-RISC vs SPARC vs Alpha, etc.
Technically, there isn't a reason why eGPUs shouldn't work, they just need drivers.