To get to the $100m target Dec17, they need to grow at around the same $ACMR increase as the last quarter which would mean percentage growth of less than 100% as you have pointed out. This to me seems conservative but nevertheless sensible in terms of not over promising and potentially under-delivering.
Historically the rate of dollar growth has increased and now that they have more capital at their disposal it could be expected that this may accelerate further.
The only longer term number that has been mentioned was about having a goal of merchant transactions of $10b which would be around 10x current business levels - therefore from this the implication is that their longer term revenue is $500m