If software isn't novel, that means some other, existing software does the same thing just as well in the same way on the same platform. So, unless it's a hobby project you're building alone, why don't you just use the existing software?
I think that writing software that isn't novel fails to be worthwhile by a perfectly ordinary, mainstream definition of "worthwhile".
So you would consider a CRUD app with some basic business rules to be novel? Basically meaning that any software that requires any development effort is novel?
That's a completely valid definition of worthwhile software, but to claim it's impossible to create an estimate to complete said development is absurd.