It’s too early to be certain, but I’ve got high hopes for the future of the SHIFT 6mq.
I believe it has mainline linux support, or it is being worked on, which will be important for ongoing OS upgrades. Otherwise they have a similar philosophy to Fairphone with an important difference; SHIFT wants you to be able to upgrade their phones, not just repair them. I don’t think this has been realistically tested yet, but the successor SHIFTPHONE 8 is coming out imminently, and I think we should start to see pretty soon if any of the new modules can be installed on the older model.
I’ve actually got the SHIFTPHONE 8 coming myself, because I got spooked by places turning off 3G already and wanted to “future proof” with 5G, but otherwise would have preferred the 6mq.
The one caveat is that SHIFT is a very small company, which could mean risk for long term support.
There is a workaround for this, which is to use a service like JMP.chat to redirect SMS to XMPP, at which point you only need to ensure internet which is a bit of a lower requirement than specific networks (but of course may still become more limiting over time)