I know this is a hard ask, but consider the Apple or Lenovo model of long support contracts. Not only does this help a lot of buyers to get your product, but you can start refurbishing trade-ins to get parts to service support cases.
In the Frame.work style you might be able to do it via a more DIY approach.
IBM used to guarantee availability of the exact chips, and did a lot of stuff behind the scenes to make that happen.
That sort of a guarantee way beyond what's reasonable of Frame.work, they don't control their suppliers to that degree. They've already updated the peripheral chips & hardware even within "v1", both for bugs and supply issues.
Frame.work has pretty much implied the form factor will remain largely untouched, so you're likely to be able to swap a component in even years from now, even if it'll be an "accidental upgrade". That sounds quite reasonable to me...
In the Frame.work style you might be able to do it via a more DIY approach.