Radical idea here, but maybe those many companies could _fund_ the development of key components of their infrastructure.

Indeed, seems like it should be pretty straightforward.

I understand why the venture-backed entity couldn't do this, but given the reactions here, could a new maintainer not take over and simply charge for support and future enterprise features like the Sidekiq guy?

Maybe but only if that gives them a competitive advantage.

There's no reason companies can't fund mutually beneficial entities. In fact, it's quite common in the form of trade associations.