What about a classic mode category where you have to beat the bonus game? And also an IL of only the bonus game would be cool, maybe split into the different characters.

That seems very reluctant considering its usually the 2nd to last stage for a majority of characters. As to a previous forum post you made that had something similar to this, I do not see anyone willing to submit ILs of individual stages in an individual game mode, adding this individually and not the other stages would make no sense, and either way, adding all individual stages of an individual game mode makes no sense in itself, even if you could convince multiple people of this idea, this is more so of a Category Extension rather than a subcategory on a main leaderboard.