It was based on Telepathy https://telepathy.freedesktop.org/. None of the built-in backends for XMPP, SIP, Skype and cellular calls used libpurple. (A libpurple-based backend could be installed from the community app repo.)

I wish Telepathy got more popularity, it seemed to be a better architecture than Pidgin/libpurple with the protocol support in separate processes etc.

Well, me too, having spent the best part of half a decade working on it! But I broadly agree with Rob McQueen's assessment of how the architecture turned out to be fatally flawed. http://web.archive.org/web/20210427061305/https://mail.gnome...

The crashes I still experience in libpurple backends today still lead me to prefer the Telepathy architecture.