Things like the rock men can be done in the regular line, so I doubt that would be a real possibility here. SDCC is an opportunity to do things that are a bit out of the ordinary, things you'd have to come up with a special SKU for in the regular line. I think Modulock would fit into that category; if he's done like Plastic Man, with lots of parts, he'd probably be hard to fit into the beast category because of price (due to tooling costs he might come in at a higher cost than even Rammy). Same with Multibot. Something like Razz and Broom would be too much for a normal slot but maybe not enough to justify a beast slot.
I thnk after the lackluster reception Vykron got last year, Mattel will go with something fan demanded this time, and it will be something a bit harder to fit into the regular line categories. That's what Mattel seems to see the SDCC exclusives as now, a chance to use the resources for something that doesn't quite fit elsewhere. Rock people, NA Skeletor, and other figures that could be a monthly choice for the sub are very unlikely. Even someone like Dare, if he were planned for this year, would likely be in a monthly slot, not at SDCC.