We have "7-speed' suggested, which to me says we are likely to get or perhaps should pre-emptively add the matching 18-30ish tags for all the other "N-speeds". The guidance from the proposer specifies that it is specific to cassettes, so I've suggested a description to make that explicit. I have tried to make it easy to edit my addition so that it could instead include rather than exclude the other 7-speed options.
But I don't know that there's a lot of point. The days when "10-speed" was a type of bicycle are gone, and if anything the categories that might make sense are the chain width ones. But then we get tags like "early-campag-10-speed" which is straying a long way from "tag:" and more into i-have-a-question-about-bikes-tag territory.
I note that we have a great number of 8-speed, 9-speed, 10-speed, 11-speed and 12-speed questions, none of which are thus tagged as those tags don't exist (yet). We also have a few 14-speed questions and more 3-speed, 5-speed and even some 18-speed and 63-speed ones.
I suggest removing the tag.
My feeling in general is to reject suggested new tags where there's no effort in the description, someone just thinks "oh, I need at least one tag. Um. bike... no, too general" so they put something random in. I've seen a rash of "X applied to bikes" tags added recently, and I think they're not helpful. At the very least I would prefer a longer description, and a bit more justification than "you can use X in, on, or related to, a bicycle". We have "carbon", "bamboo" and "steel" for example, but not "plywood" or "plastic", and the usage of those tags is extremely erratic (there are at least 5 questions about bamboo bikes that don't use the tag, and only 4 that do).