It looks like Facebook could be resurrecting Googlle's Project Ara, which was cancelled in 2016. It's still unclear how a modular device would fit into Facebook's business model, but the company certainly acquired key team members that worked for Google's Project Ara and also Amazon's Alexa speaker.
https://www.notebookcheck.net/Facebook-could-be-working-on-a-modular-smartphone.236704.0.html