how are instances supposed to handle 300k new users overnight?

They won't. Not at first. First we will get maybe 50k, LW will do their thing and try to gobble up the majority of users, alien.top can also help absorb part of this crowd and I could even finally convince some other admins to set up fediverser on their instances to help with the migration.

But the important thing is that this type of backing from the mainstream would mean free marketing.

do you expect those hundreds of thousands of new users to get a Communick subscription?

All of those people, of course not. But I expect the increased user base and media attention to bring the following:

• more instance admins realizing that this is not sustainable to be run as a hobby
• power users who want to run their own instance
• companies looking to establish their presence online (therefore looking for a quick/simple way to set up an instance)
• increased usage in the topic-based instances, which can open potential revenue streams.
• more people realizing the limitations of the server-centric approach and becoming interested in a single "Social Browser app"

All of those things translate indirectly into more business opportunities, none of which need to sacrifice the ideals of the open social web.