Mastodon is very resource heavy, I couldn't get it to run on a raspberry pi 3b. Pleroma is an alternative to mastodon that is very light on resources, I'd recommend that personally.
I think the main issue of Mastodon is that its search completely reliant on elasticsearch, while Pleroma tries to go by only with PostgreSQL FTS?
Even if SQLite JSON isn't sufficient it could be realized with string columns for now, and indeed SQLite is recommended by Library of Congress for archival storage and used by iPhone so I think it's a solid way to expand Pleroma even if native JSON is not sufficient.
If anyone wants to pay me to do this as open source I'd jump, contact in bio. I don't know Elixir yet but am motivated and have 15+ years of dev experience in all kinds of systems, and experience in the adjacent parts.