Anycast IPs would be lovely, but they're tweaky enough to use that I suspect the support burden would be high (since they suck for long lived connections). And they're not nearly as easy to provision as a complicated DNS setup.
They need to just stop having region wide outages...
Seems unlikely. Not every AWS user is in every region. They would need to have a separate range of anycast IPs for every possible combination of regions (2^N possibilities) to prevent packets from going into a black hole. If they wanted to be able to serve a conservative number of hosts in every region (say 32768) that would require 15-bits of IP space per combination. If AWS expands to 10 regions, that means 25-bits of the IPv4 space. A /8 only gives you 24.
I guess an alternative might be to do some kind of NAT for unbound anycast addresses which forwards packets to an available region, but that is hugely complicated.
I'd be delighted if they offered it for even just two regions. Right now if you want your service to be highly available you either run your own routers in two collocation facilities and forward to AWS, or you don't use AWS.
There's still no good high-availability story for region-wide outages, and there won't be until they do this.