I've never seen the machine (yet) but it looks like the group cools and it's the shot that warms to temp.
So if you pull back to back you would overheat at some point but they say after ~3 min you stabilize and after 10 min you might want to do a warming flush. So unless you have preloaded baskets on a one group it might be pretty stable.
But I think Mr. Roboto has talked me into the 2 group and then the ability to go group to group (and back again) looks on paper like you could pull back to back shots until you run out of water.