Well, I'm new to the cryptocoin world. But still much earlier than the general population!

From my own opinion, Bitcoin would not be the default digital currency of the future as there's quite a bit of future for it as a wealth holder i.e. gold as there's a number of issues with the current system for the general mass adoption e.g. no instant transfer. Gold is very good comparison to Bitcoin. A big currency in the past, now retired as assets. Satoshis will definitely worth a sizeable sum with mass adoption . As for the likely candidate of the default digital currency... I cannot yet see one. 

-W