The M2200 seems to represent something of a sweet spot in monoblock amp pricing and power. A larger monoblock would have a correspondingly larger price tag, and may not be as likely to find as large a market. Of course, the 790 is going to have a price tag somewhere above the 770 and its successor, and the sheer power demands of that amp will require a lot of infrastructure to support (I'm figuring that the only way to fully utilize a 790 is to have two dedicated circuits in place solely feeding the amp), so maybe there is some interest in developing an amp for a smaller market segment.

As for the actual logistics of it, there are a few options. I agree with Ritz that the existing "pizza box" 1U approach would probably become difficult to sustain in a 300W @ 8ohm design. They could do a monoblock in a different cabinet, though. For example, Marantz and others have done monoblocks that are roughly 1/3 the standard component width so that three would sit side-by-side on a shelf. Since the M200 and M2200 are a completely different design than the amp modules used in the Outlaw multichannel amps (both the 770/755 and the planned 790), the 790's amp modules would not be able to migrate to a monoblock without some sort of significantly different cabinet design such as the 1/3-width form factor (which would likely retain the height and depth of the multichannel amps). Even then, I don't know if there would be room for a sufficiently large toroidal power supply in such a cabinet if it has to feed a 300W amp, but I'm just a mechanical engineer so it may not be as hard as I'm imagining. Maybe a half-width chassis? That would even let the amp module rotate 90 degrees and possibly reduce the height of the cabinet. Digital amps may also be an option, but that technology is still in the process of evolving - with Outlaw's fairly extensive array of solid state amps, I doubt they'll enter the market with a digital switching amp until it is a bit more mature.