Can SST-50 be directly driven by an 18650 ?
Yes, but you have to watch out for overcurrent and make sure to use thick wires if the current is to low. : )
Or you might try a Sandwich Driver [ combining 2 drivers ]
I was thinking of going SST 50 , + Sandwich Driver , and then see how much current a single 18650 could supply ...
Some folks are combining 3 or 4 1400mAh drivers with the SST , to get voltage regulation + current , 3 x 1400 would offer 4200mA potential and regulate the voltage ..
As to whether your 18650 could supply such current , that is the question ?
Most cells I have tested are limited to around 3A or worse , the only cells to really push harder = Panasonic 2900 and Samsung 30A [ 4.35v ] ...
So if your not prepared to buy the very best cells available , it may be pointless ...
The XM-L emitter looks to be worthwhile waiting for ...
Supposedly, running two the of DX mc-e drivers (~2.3A each) together works. http://www.dealextreme.com/details.dx/sku.20330
Running direct drive is just ghetto. Even if you get one that works fine on a IMR, it'll only maintain that high current for 5-10 min.