I tried to read threads about this matter but some are very old and there are new kernel power releases and decided to ask about the current situation:

Is it possible to use N900 as an external monitor and keyboard for another device?

If yes, by which way of connection?

a) usb port

b) bluetooth

c) wifi

d) some other, what?

I read about usbIP but could not find where did it end and what you could do with it.

I just thought that now that we have very very small usbsticks with whole live distros and raspberries and such that can't it really be possible to run one like that and use n900 just as the screen and keyboard? There are some further questions which will come later.