None of my comments are TCP specific, but as I said - at 3 PoPs, you won't see routing weirdness; announcing the same prefix from 70 PoPs will cause the likelihood of route instability to increase. For the case of UDP, hopefully no one will notice, as your lost packets will just go to the next available route; for TCP connections, a route withdrawal sending you to the next nearest PoP will lead to a broken connection and clients seeing badness in their browsers.

Anycast is an IPv4 quirk in that it wasn't designed; it "just works" because of the BGP route decision process. Yes, you can announce your prefix out of multiple PoPs, but how people choose to use the routes you announce is where things get "quirky".

In theory there's no difference between announcing a /24 IPv4 and asking us all to accept it, and doing the same with a /48, but in practice you'll burn an unacceptably large amount of IP space, IMHO, and if you tell ARIN that you need a second /48 block because you burned your first with less than 25% utilization, they simply won't let you have it.

Disagreed on your last point. The abundance of prefixes isn't the problem IMHO; it's the acceptance of route announcements from upstreams. If upstreams were to start accepting and passing along more granular routes, maybe we'll start seeing more anycast deployments, but I doubt it.