well, basically not much to choose from is left nowadays. iOS would be like the stark opposite of maemo. WP never had true value and is now deemed to rest in oblivion with the latest move done by Microsoft. sailfish, obviously, would be the closest choice as a maemo-successor; however, if you want to be more 'conform and compatible' to the 'mass', android isn't too bad either. most phones are capable to run an aosp-derivat. for what I know, cyanogen is entirely open source; the google-apps would be closed source but it is not mandatory to install them. for me, the true distinction to the 'rest of the world' has always been the neat keyboard and the resistive touchscreen. I'm afraid, nothing similar is available (why??). however, a small BT-keyboard may be able to provide some 'relieve'. (just my two cents regarding a follow-up phone)