Perhaps...but let's be careful about the term "releasing". That implies there's some kind of finished material to release. Is there some kind of indication that they have a couple albums of material "in the can" that's just sitting there waiting to be released?
I think it's more likely that there's a lot of half-finished ideas, partial takes, etc. the band has yet to fully develop. Even a lot of the "b-sides" from the latter part of the decade that did see the light of day sound unfinished...so I'm not sure why anyone expects the legendary Songs of Ascent stuff to be any different. If it's even that finsihed.
In any event, if it's not out there, we can't really count it as "productivity" can we? That's like saying an artist is "productive" because she has a lot of half-finished paintings. "Productive", by its definition, means to "produce"...not "work on". By any metric, U2 doesn't produce material at the same rate that they did in the 80's and 90's. We can only speculate as to how much they've actually done.
I agree with your comments on NLOTH, however.