Everyone should probably be using apps like Signal for all comms. I loved iMessage and while some of my security contacts use Signal, with this change there's no good reason not to shift as it's multi-platform and has solid end to end encryption... at least for now.I can see this pushing even more users to Signal, for better or worse.
Unfortunately with Apple finally rolling over (the 800lb gorilla that has been fighting the good fight for user privacy and security globally) it's quite likely we'll see other companies following suit and building in robust surveillance mechanisms and backdoors, as well as governments feeling emboldened to pass legislation mandating backdoors. A lot of companies pushed user privacy and security mostly to compete with Apple... with Apple backing off, so will the industry. Unfortunately these backdoors will be used by nefarious actors of all sorts (not just nation states) so the net effect is a much less secure and private mobile ecosystem.
Where this ultimately leads, I don't know, but it's a dark day for users everywhere.