I would assume that keyboards, trackpads, etc. will also be available as some laptops bite the dust and are scavenged for parts.
Whether the motherboard/CPU will actually be upgradeable obviously remains to be seen. The 11th Gen CPUs get a lot of flak, but they have good single-core performance which will make them suitable for general use for a long time.
It's at least equally upgradeable as the first ThinkPads with soldered on CPUs, which by today's standards is still pretty good - and if framework deliver on their promises, then it will be even better. But either way the baseline isn't bad.
I mean, you can buy a new-ish Thinkpad where you can replace/upgrade all of those things. You get great compatibility and most hw/sw compatibility bugs are already known and have workarounds. Framework has to have some other value propositions as well besides being able to replace things you mentioned.
I don't own one personally, but reviews have been overwhelmingly positive so presumably it does have something to offer beyond replaceability. (disclaimer: some people on HN seem to have had some driver issues on Linux on theirs)
Quite the opposite. That would only apply to a very popular laptop like some thinkpads.