What is the actual support to this statement? Have you tried using Sailfish on the first Jolla smartphone coupled with the TOHKBD? It was actually as close as it gets to a N900 experience in my opinion, except from the general bulkiness, the concern of dropping the phone when it just holds with magnets, the fact that I still preferred the feeling of the keys on the N900, and the lack of stylus (but admittedly none of these limits were related to the OS).

As for the slider mechanism, Chen knows where he's headed according to the details he gave before (close to the mechanism already seen on an HTC device, with tilt adjustment and not just a slider). Not saying it will be easy, but at least he knows exactly what difficulties he will face and probably has a plan on how to circumvent them.