@jeremiah Not to derail the thread, but could it be that the original question might need clarification?
There seems to be two views here: “technical” and “experience” (or select other names). Those leaning A make good points on updates and keeping OS usable. Those leaning B want assurances that (at least basic) functionality does not change often, nor much and can be relied on. It might be a good idea to open these up a bit for clarity. I also think that the attitude towards a phone may be different than towards a laptop or desktop regarding this, as people depend on a phone more, which is factor to consider.
Are some parts going to be stable - can they be kept stable (if so, the rest can perhaps roll around as much as wanted or needed)? What would stable-rolling cycle be: daily, weekly, 3 months, 6 months, 1 year, 5 years… - what is too long, what is too short, what would be a good middle ground?
[edit: also a tangential connection to lifecycle conversation How long is the lifetime of Librem 5?]