One thing that's changed since this suggestion was previously looked into is that
nonogram is now listed in
Wiktionary:
(games, puzzles) A puzzle in which cells of a grid must be filled or left blank, according to sets of numbers given at the side of the grid, to reveal a hidden picture.
In view of Wiktionary's all-inclusive policy, this is not a very strong argument for accepting the word in Chi, but it helps.
I noted, when I considered this in 2009, that the word was sometimes written with an initial capital letter, but from what I can see, it's usually written in all lower-case letters.
It appears so infrequently in the corpora that it's hard to say if there's been any trend in how often the word is used. But the
Google ngram viewer doesn't show much change over the past thirty odd years.
If
nonogram was a word used by anatomists or stockbrokers - or even by bird watchers, pat - I'd probably rule it too obscure. But since its specialist field is puzzles, meaning that quite a few of the Chi community may know of it, I'm willing to give it the benefit of the doubt. So
nonogram will be accepted in future, as a rare word.