XMPP accounts in combination with a hosted https://movim.eu/ would be excellent. The creators of movim are seemingly quite minded towards data independence, so maybe they’d be interested in this too? It couldn’t hurt to drop them a line if there’s never been contact between IH and movim devs before.
An XMPP account (usable via pidgin for instance) would indeed be a great add-on for the indiehosters basic bundle for 2018! That would be super useful to get more independence from the GAFAM
PS: not sure whether I should post this on the “features” page?