I looked at the Blunami on the SoundTraxx website and watched their video. Did I miss it, but have they come out with a Blunami for O scale yet?
Not yet. The number would be 4400 as opposed to 2200. However, the 2200 is a 2-amp stall-current decoder which would probably support small O scale single-motored engines (provided you don't stall them, of course). Last time I ran a four-powered train at the club (4 MTH diesels) the draw at the transformer was just under seven amps -- 1.75 each for the 50-car train that was in tow.
Theoretically, the 2200 could probably handle a two-motored china-drive engine. Taking one of those engines and series-wiring the motors, the current draw would be cut in half and you'd be talking about an 850-900mA draw from the engine. That's well within the limits of the decoder. Dan Dawdy put DCC H.O. decoders into a quartet of RS1's with series-wired China drives.
The more I think about this, the more I'm on-board with the idea. As for a voltage source, it would be easy enough to put in an on-board voltage regulator inside a diesel to limit the input voltage to the decoder.