Hi guys, I was brought to this thread by James and as a double bass drum player myself. I'll reply accordingly.
There are pros and cons to both, having a double bass drum and a double pedal with a single bass drum.
The pros of a double bass pedal on a single bass drum besides the obvious, carrying a pair of double pedal is better than carrying two bass drums, would be you don't have to tune two bass drums to be exactly the same tuning which would be difficult to attain.
Having two bass drums, Besides the visual aspects would be, you can set two individual bass drum "single" pedals to be exactly the same tension as opposed to having a slight lag on a slave pedal when playing a double pedal.
With regards to playing constant quick notes on the single bass drum with a double pedal on a single bass drum, when playing at a really really quick tempo, most drummers use triggers, as that is one of the best ways to get the bass drum sound to really come out and be as precise as well.