No, you are limited to 1 Amp for surrounds. As to using more than two speakers with a single Amp, I would not recommend it. Surrounds are directional, and diffusing the directional cues to more than one point source will ruin the effect.
As to allowing more wireless surrounds in the future, that’s a question of physics. The current 30 ms buffer is right on the edge of where lip sync errors can be noticed, and how much bandwidth that small buffer can handle without causing reliability problems is very much a limit to how many channels Sonos can send out wirelessly.
