What do you mean by 'not so open'? Do you think maemo/meego are fully open? If yes, you are very, very wrong. I will give you some examples on the N900's maemo - camera app, music player, phone app, calendar and many many more are not open source.

PERSONALLY What I need from a 'open' phone is

1.Based on Linux
2.The ability to tweak files inside the phone, modifying system/settings files

and if jolla devices or any other newer OS doesn't offer me that ability I will stay with my N900, even if it has to be forever!