I think this is a worthy goal (maybe I would rather call it “Make TOH electronics fit a range of devices”).
To achieve it, Jolla would have to define a couple of device outlines (e.g. small phone, big phone, small tablet, big tablet) and define where the interfaces are located. With interfaces, I mean connectors, attachment points (for mounting PCB in TOH) and keep-out areas.
This is hard.
Attachment points could be in the same locations on a small and a big phone, and a tablet could have additional attachment points for bigger PCBs.
But then it gets hairy. Space is limited and components can’t be placed arbitrarily, due e.g. to thermal and radio frequency considerations.
There is a substantial risk that you lock the interfaces in places that are difficult for future devices, especially smaller ones. I would not expect current TOH electronics to fit a new Jolla Phone for the small-display crowd.
But, as I said, it is a worthy goal.