There are technical challenges, but I think the biggest challenge is the business case.
Nice to see that someone can get it right.
Boeing have identified a potential
gap in the market, but have said themselves that they have not yet constructed the business case.
A number of airlines have publicly declared an interest.
Is it enough compared to the other options available?
Are they declaring interest in the same option?
Is the "gap" actually really big enough to justify the investment in a "preferred option" to fill the gap?
We don't know the answers to those.
But Boeing also have to deal with:-
the question of cost of production
the likely impact on their own models, like the 737 MAX or 787.
Will an appropriate engine be available?
Will it have the necessary SFC and operational economics?
To answer the opening poster's question, Boeing are clearly doing the right thing by not pulling the trigger until they can get all of these planets to align.
For me, it doesn't feel like a simple task at all.
They are clearly fighting hard to use their economic strength to maximise the "gap", by threatening the A330NEO
That suggests that they are not yet comfortable with some of the market parameters of the "gap".
It also suggests they don't think that MOM on its own will "kill" the A330NEO. It will need help from the 787.
(IMO it will fail in this particular task anyway, but that's just my opinion).
Contrary to the opening poster's view, I think the LAST thing Boeing need to do is rush MOM to market without having strong confidence in the business case underpinning it.
That is clearly not there yet.