x86 computers could continue to exist for high-end users, but typical-users might be content with a hybrid tablet/computer. As ARM increased in power, x86 might dissapear entirely.
Your comments on Windows compatibility/virtualization are spot on. Cloud streaming, Citrix/XenApp, can help in some situations here. In a few years virtually all major apps will probably be cloud/browser based (Microsoft Office, Adobe Suite, streaming games/apps, etc). Windows on Mac might not be as important then. It's possible Microsoft might release ARM Windows too (besides RT). If ARM gets popular in the datacenter you may see Windows Server 2015 ARM Edition. They've done this in the past with Itanium.