Exciting software can't come without reasonably capable hardware. Expecting miracles from low end hardware is irrational. Sailfish with a few apps open is anything but a fast or smooth experience on the existing hardware ... and it's only likely to get worse as the level of complexity and resource requirements increase (as per 1.1).
There's every reason to abandon the existing TOH shape, size and fit. It leads to a blocky, ungainly phone with extremely poor environmental sealing.
Also it means another completely bespoke package for the phone, which their OEM has to work around. If they share basic physical platform with other phones, or slightly modified, costs are considerably lower and QC issues are unlikely to be as bad.
Besides ... are you seriously expecting Jolla to use exactly the same camera and lens? No? Well you'll need to cut a new hole in all your TOHs for a new camera on a new Jolla phone.