I expect that should be fine, but there’s a URL signature scheme that is apparently involved, I’m worried that should I turn up a new instance, it won’t federate with e.g. mastodon.social

If Twitter were a store, people would have no problem boycotting it. I think the mentality change that is necessary for the 2020s is that you have a choice where to “spend” your generated content, just like you have a choice where to spend your money (ostensibly at least: ISPs, privatized utilities need not apply).