So in reverse order:

The fediverse to me will always be an expanding niche, I don't think the network effect social growth works without cash. If your looking to measure by quality of dialogue instead of growth I think this presents the best option. There's plenty of economic benefit beyond ad sales from good discourse.

Instead you're looking a million AOL install disk moments until ubiquity, if it doesn't fall apart first.

Instances shutting down is actually markedly like the way famine, war or anything else beyond my control as your average user would have pushed us to other reps. You can pick up and move, but how much of your stuff? Open question. Long term it should be feasible for your own instance to fire up, fetch messages and close again, so in theory you could keep all of it.

Now hardest: scale and cost, which I'd really contend are the same problem. If you look at how such systems are introduced you find advocates for vanguard, reps, workers tribunals and nothing quite ever sticks without some lingering problems. And the reality is the web of our modern universe isn't going to independently operate with anything.

I don't think anything but a charitable model gets it off the ground, the same way I don't think the Internet is a thing without the crazy good folks running BBS boards. But it should be institutional as broadly as possible if you want long term success and trust in platform.

I think perhaps you may be confusing nobody to assert ownership of the bits, with the supposition that there is no cost on delivery.