As I have no Jolla I can't tell from my own experience what Jolla/Sailfish lacks compared to N900/Fremantle. I just can tell you what has stopped/still stops me from buying one:

- no HW keyboard - I guess that's solved with TOHKBD, in fact this project is the main reason why I still follow the Jolla/sailfish development at all

- not fully Free Software - the N900 makes me jump through hoops because of this every day and I hate the N900 for this, I won't make that mistake twice, so no Jolla for me before everything is Free Software.

- no way to run desktop programs - actually Easy Debian was a very important reason why I bought an N900 in the first place. I'm not fine with someone porting them to Sailfish unless that someone can port and reliably maintain(!) more or less the complete Debian main repo. This increasingly hypothetical someone would not be me.