There will be some destinations that rate 3-cabin service. Those destinations will see 3-cabin aircraft. Other destinations don't have that demand and they'll see 2-cabin aircraft. It will be less about what was flown previously and more about what the market supports going forward. This is already being seen in some TATL markets, the Pacific theater and the IAH-LIM route. Expect to see more of those sorts of changes in the future.

As for the TATL speculation you've made regarding the 752, there will still be plenty of those. We might even see some show up for routes ex-ORD to secondary UK or Ireland destinations as the range shouldn't be a problem. But there will still be plenty of wide body aircraft across the pond as well, both for the markets that need the 3-cabin service as well as for those with higher capacity demands that the 75s do not meet. And there's the range issue.