Looking beyond the Osprey for Merlin's eventual replacement

What sort of aircraft could replace Merlin?

A later-generation vertical-takeoff aircraft, possibly beyond the Osprey's immediate successors.

Merlin's eventual successor was expected to use a later generation of vertical-takeoff technology. The 2020 forecast looked beyond the Osprey and even beyond the Osprey successors then emerging. A second- or third-generation aircraft was considered possible. No particular airframe was identified, so the idea concerned the technology likely to be available when replacement became necessary.