I think the alternative mutual fund could have one stock, if the manager was willing to structure it that way. It would not work like regular mutual funds with daily prices, diversification, etc. It could even limit liquidation events to correspond to TSLAP. But it would aggregate current individual shareholders into a large group that is a single shareholder. This type of fund would not have much appeal to the typical mutual fund investor because it is not diversified. But it could be an SPV to accomplish Elon's stated objective. And it might not need to be limited to accredited investors - what I read on the SEC site suggests that it would not require accredited status.
Fidelity, under normal circumstances, probably would not have much interest in that. Doesn't appeal to their target investors who are looking for diversification. But it would require little management (nothing to manage, really) and would allow them to stay in the game as the stock appreciates and is ultimately re-listed. Honestly out of my depth on this theory, but I don't know why that wouldn't be an option.