I've seen lots of successful large k8s installs. This same argument from the nomad crowd comes up constantly. There's a reason why nomad lost, and it's not because it's better.
Which is also bad compared to 5.3 codex. People don't seem to realize that this is not codex 5.3 quality. It's a large step down on the benchmarks to get lower latency.
That's a claim musk made, but they already have over 500 launched without them. They should have 1000 by year-end, so it's unlikely they'll be able to use them for a couple of years.
They do not have cross-links. They were in the original public announcements, but none of the current satellites have them, nor have they announced when they would be launching some that do. It's likely years away.
Possible, yes, practical, no. In general, you want the least complexity as possible in the payload, since you can't fix it as easily as you can with ground bugs. Also, memory that's space-hardened is going to be significantly more expensive and failure-prone, so you need a lot of redundancy.