I'd have to disagree. The N900 case is good, but if better cases are more available and could have:

1. 4 row bezel-less keyboard.
2. CBD-type anti-reflect display
3. Higher capacity, cheap batteries.

... then use the better cases.

I feel the need to point out that the demand for this is enthusiast-only and probably short-term (someone will come out with a HW kb Jolla/Nemo phone sooner or later).

Is there much point adding things that will never be supported? You need to first establish a price point. This involves anticipating demand because obviously you need to be sure of selling 200+. Looking at poll, aim for 300 Euros or lower...

Then fix the feature set and don't be tempted to mess with it too much later. Then start taking pre-orders a la Kickstarter.

More sophisticated devices could be built later once you've established a track record of actually getting a phone out. No disrespect but let's face it: it's so epic, it's hard to believe.