The friction is both what we experienced as part of adoption and in my personal experience. Actual personal experiences may vary, of course.
I didn't realize you were involved in this company until I read your other comments. It is unclear what "You're locked into some of our custom components" means. Can a average techie, maybe someone who is comfortable opening their laptop to add RAM or new storage but wouldn't be comfortable making any other hardware changes, upgrade this with off the shelf parts? If the answer is yes, that should be in your marketing material. If the answer is no and you can't commit to selling these custom modules, then I stick to my original point.
Yes, about as easy as opening a laptop. Unscrew some screws, lift a cover, install a new M.2 SSD or whatever. This is a picture of the "standard" assembly: https://i.kane.cx/NFIpf4 -- compute element slots into a connector, and there's the standard M.2 slot etc. Ours won't be too different, just a different form factor/connectors/additional features.
We're committing to selling all custom parts for at least a few years, but I can't give a hard number on how long. I'd say 4 years for sure.