Originally Posted by
BobZ
You're probably right.
The evolutionary step beyond the hi bypass fan engine has been conceptually understood for a long time.
They played around wth UDF testbeds but its turned out to be a much longer term solution. Its quite the accomplishment.
I think the bigger question is whether they will be able to build an engine like that with what we now see as standard reliability and maintenance intervals from a turbine engine. Some evolutionary steps were understood but were never really implemented or were on a relatively small scale because by the time they could be built the next propulsion step beyond was also feasible. See turbo compound engines and the Napier Nomad.