Android Enterprise Recommended Rugged Devices 9.0 - 10.0 are supposed to get 5 years of security updates. Unfortunately, Google dropped this requirement in its Rugged Devices 11.0 spec. Of course, this means that the phone has to be upgraded to a newer version of Android, since Google only provides 3 years of security updates for each version of Android.
Some of the phones in the list aren’t really getting 5 years of updates, but they are pretty close. For example, the Sonim XP8 was released in April 2018, and its web site claims that it will get security updates until December 2022, so it will get 4 years and 7 months of updates.
I doubt that the Librem 5 will get 10 out of 10 as long as it doesn’t offer replacement parts, but it should score pretty high.
While I think the modular parts with pogo pin connectors in the Fairphone are an awesome idea, the ability to easily change/upgrade the cellular baseband and WiFi/BT in the Librem 5 is far more important in my opinion for the long-term use of the phone. I foresee a lot of spectrum changing its use in the next couple years with the shutdown of 2G and 3G and the way 5G will push networks to shift LTE to TDD bands to save spectrum space, so the ability to change the cellular modem will be very useful.
Modular cameras made sense in the Fairphone 2, because it allowed upgrading from a 5MP to a 13MP camera. I don’t think that the i.MX 8M Quad processor can support much more than a 13MP camera and cameras in smartphones don’t often break, so I don’t see much point in making them modular in the Librem 5. I can’t see anyone wanting to upgrade the Librem 5 sensors and they rarely break.
The things that people will want to upgrade (the processor, RAM and eMMC Flash) are hard to make modular inside a phone. In my opinion, it would be better for Purism to design the main PCB in the Librem 5 v2 to be backward compatible, so it can fit into the Librem 5 v1, and to sell the main PCB as a separate part than can be used to upgrade the Librem 5 v1. The SHIFT5.1, SHIFT5.2 and SHIFT5.3 from ShiftPhone were all backward compatible in this way to allow upgrading.