I don't see NLP listed on https://linguistics.stackexchange.com/help/on-topic How about adding it?
The problem with expanding an on-topic list is that it encourages the mistaken conclusion that anything not on the list is off-topic. My opinion is that there is already too much superfluous overspecification, such as a distinction between graphemics and graphetics; phonology and morphonology; linguistic anthropology and anthropological linguistics. Since "prosody" or "agreement" aren't explicitly mentioned in this long list, one might mistakenly conclude that questions on those areas of linguistics are considered off-topic.
I am aware that a terminological distinction is made between NLP and comp-ling, and I still don't understand how NLP isn't just a subset of what is covered by CL. If you can point to a question that was closed or otherwise deprecated because it is "off-topic" and yet is about NLP, that might make a case for clarifying that NLP is on-topic. As I imagine you have surmised, people don't exactly stick to strict and literal interpretations of the off-topic list.
I'm not trying to threadjack your question, but by way of comparison, I think that there is a problem with the treatment of a certain class of questions in the area of descriptive linguistics (which is not part of the explicit on-topic list), and that is when people ask questions about facts of languages, they are frequently closed as being off-topic ("language-specific"). These are generally not great questions anyhow, and the ones that are are contextualized in terms of a theoretical linguistic notion and not closed. It is possible that some of these questions would survive if "descriptive linguistics" or "language description" were added to the on-topic list. OTOH, anything that you would "describe" about a language is going to be about the syntax, phonology, phonetics, morphology, graphemics.... of the language, so already covered by an existing category. As long as you don't equate "syntax" with "syntactic theory", etc.