There already is one on mobile: https://github.com/TwidereProject/

You can use Mastodon cross-poster[0] like Cory Doctorow[1] does.

[0] https://crossposter.masto.donte.com.br/

[1] https://mamot.fr/@doctorow/100397875390621221

This never works, it just means people don't actually switch at all because in the end they only engage with one place properly. This was one of the things that went wrong with app.net.

A ton of people _hate_ crossposting accounts.