edit: Eugen, you can steal this business model from Twitter if they don't want to play in this space. Run Mastodon-as-a-service and sell it to institutional actors. I don't know who runs Masto.Host but they seem to be positioned to offer your software as a service to these groups.
There are other AP implementations that can be sold (as a service) to these large pocketed groups, not just your own software product.
another edit: this may leave a sour taste in your mouth but you now have a notable political user of your software, one that more than likely does not have the technical competence to be running it on their own. Someone could be making money off of them by providing a managed, white-labeled Mastodon instance (and then be responsible for scaling, security, availability, all the devops shit, etc). Not saying that should be you, but someone could.
There's value in managed services (security, keeping updates applied, uptime, scaling, etc etc)
If there's someone at Pixiv reading this and looking to pivot, I won't feel bad if you take this idea and run with it.