Here's what we've got so far:
1) Major legacy bank exchange
2) Amazon.com
3) Usable software
4) Remove overhang (e.g. FBI coins)
5) Systemic/national financial instability
Here are some more:
6) Favorable regulatory change (e.g. China wises up, or India)
7) Killer app gains traction
Remittance network adoption curve inflects
9) ETF opens in U.S. or London
a) Leading investor takes large postion
b) National police/spies/military accumulate tactical holdings
c) Central banks accumulate strategic holdings
It would be useful to estimate pdf vs. time for these and any more suggested