Please, don't make a phone that implicitly requires a holster or case or screen protector. These things are perfect for people who think they are perfect, horrendous for people who think they are horrendous, and there is no proper way to reconcile these two groups. It's just a matter of preferences and they can hardly be discussed. Just don't make a device assuming everyone would use such protections (and they would still provide increased protection for those who want to use them, but won't be mandatory).

I hate the screen protector on my Jolla C, yet I have no choice. I don't think this is a good design to make it obligatory because the screen itself is not scratch-resistant. I hate rubber case on my N9, but I did not have to use it (acceptable protection trade-off), this was optimal.

As for keyboard diacritics, I agree that an equivalent of Fn+Sym to show special characters on screen as on the N900 would be good, but this does solve the real issue if you need diacritics every two words in your language. It's perfect when you need the special characters every now and then, not more. But it's still good as it shows all characters, so it definitely has advantages. But for everyday typing, there is nothing like the 2-key or 3-key combinations that DrYak just described, or even better, dead key followed by a character, without compose key, like:

' + e = é
` + a = à
" + o = ö
^ + e = ê

This is how us_international works (both Linux and Windows), and it also allows using diacritics on capital letters, which is good. Basically with this, in French you just need one key to map ` and you can type every French special character with dead keys, since ', " and ^ already exist on every keyboard layout anyway, even simplified keyboard-slider layouts. You'd need Alt+key combinations for æ, œ and ç though, unless new dead key combinations like ` + c = ç are created (this should be a non-issue if layouts are flexible as they are on desktop OSes).

Of course us_international does not mean us_french, so I can also type things I don't need in my mother tongue using the same system, like åøóßš, which ultimately reduces the need for extra keys in every different language. Nonetheless, this only works well for people who are used to qwerty, so unless they are already using it or determined to migrate to qwerty regardless of their native layout, it will be hard to make everyone happy. I just hope it will be possible to customize the software side of the available layouts this way so dead keys can be used just like on Linux or Windows.

About grid vs offset keyboard, I admit having no experience with thumb typing on an offset keyboard but the discussion shows that the final decision will be hard and important. Overall I would still naively think that there is a reason why most thumb-keyboards were arranged as grids, but to be honest a lot of these keyboards were crap anyway. I'm just afraid the same with offset would have felt even weirder. Livermorium may have the experience there, let's see what they think is best for thumbs and blind-typing (but keep thumbs and blind-typing with minimal movements in mind Chen please).