While this might be a decent option for a medium that could be considered important for public discourse, it's certainly not going to goose your stock price and I'm guessing even every Twitter user contributing a few bucks won't get you to a sale price that might work for the board.
While I agree there is no shareholder value involved, I think there is some scope for thinking of the platform as a public utility and putting it under some framework other than a publicly traded corporation. It could operate either as a Foundation, a Public-private partnership, a federal agency perhaps as a subsidiary of the Library of Congress, or some other system of governance that makes it operate more as a public trust than a corporation.
It's function is definitely more akin to a public utility than a product produced for market, after all, so why not? I'd say most online stuff still has too many returns to innovation to where the opportunity costs of nationalizing them outweigh the benefits. But clearly Twitter isn't doing a great job of staying afloat as it is.
Because Twitter is a US-only thing, right? Don't forget about the enormous _global_ user base who would definitely not be served by making it directly controlled by the US government.
I suppose there might be some other sovereign wealth funds and investors from China, Gulf States, UK, etc. in there too but still, hardly representative of its actual user base.
I agree that that would probably be the worst option of the bunch, but it's just an example of other ways a platform can be governed that's not a for-profit corporation.
I could also see this becoming a common thing for blockchain based services since Ethereum contracts would make this a very easy thing to do.