I hate the idea of subscription-based gaming, but I think in cases like this, crosswords and other similar puzzles, that a subscription model might really work out for the best.

Treat Picross like the daily crosswords of a newspaper. Release a daily puzzle, and maybe let people download all of the past 7 days so they can still catch up if they miss a few.
One free download with a few hundred puzzles, and then subscribe. (Or alternatively, a single entry price which works out at the same as a couple of year's subscription)

Add in daily crosswords, word jumbles, wordsearch, sudoko..
Call it "The Daily Puzzle" or something..

Nintendo should TOTALLY do that..
.. Or maybe bundle THAT in with the upcoming Switch Online Subscription fee..

Come on, Nintendo!!!