I think the path to power goes through the south, but it is the Big 10, not the SEC that can do more with that.
The SEC just doesn't have enough good targets left to make a geographical power grab, they'd rapidly see a reduction in per school payouts if they were try to do that. For instance, after the very logical choice of Virginia and North Carolina, you'd end up with something like Pitt, Cincinnati (Big 12), Boston College and Syracuse. These are middle of the pack ACC schools, a conference which pays out about half what the SEC does.
On the other hand, the Big 10 could go after Virginia and North Carolina as well, but then chart a path toward more lucrative territory, for instance Clemson, Louisville, Georgia Tech, and Florida State. These trend towards the top of the ACC in earnings, and not only that but it's a far more direct threat to the SEC's regional dominance.
Furthermore, since they're already established on the west coast, they could realistically do something like go after something like Arizona and Texas Tech as well. The SEC is already in Florida and Texas for example, the Big 10 simply has more territory they could turn into "battlegrounds" than the SEC can. This means if things heat up between the two, the SEC likely has to adopt a more defensive posture (doubling down on territory they already control) while the Big 10 can adopt an offensive posture (moving into new territory).
Having said that, it's not something I see either party as wanting to do because they'd have to share TV revenue with the new schools. So yes, it is basically waiting for the other side to screw up and then take advantage. Or, of course figure out how to cooperate and sort things out.