The current policy we established is actually detailed in this post, albeit not containing all arguments on the subject. To summarize, our policy is that genre tags, like platform tags, are only used for question that are about that genre. That is rather what tags are for, after all - even our sub tags.
Should probably cycle out that post you found or otherwise note that it's been superceded as of late.
In a technical sense, genre tags aren't actually a proper form of tag when applied to a gameplay question. They're actually a kind of subtype to a meta tag in that it describes a tag, not the question as a whole. In fact, the fact that the game is an RPG is relevant to your interests in a way that is wholly dissociated from the fact the question is about that game. It essentially is a guidepost for you to find games that may interest you due to the genre, not to help you find questions that'd be of interest to you. Every question about that game would have equal appeal to the person who is interested in that game's genre.
Essentially, the tag's utility is redundant with the game tag, and its only advantage would be telling people who don't know that the game was of that genre. And that's not the responsibility of an extra tag, or our question base, to do that. It'd be like coupling [c#] with [object-oriented-language]. Yes, there are far more gamers who are interested in specific genres than there are programmers who are interested in specific language forms, but the utility remains dissociated from identifying the problem of the question, which is the core job of a tag.
The tag limit argument is something better understood if you take into account that platform tags would have to operate in the same fashion. After all, platforms are static and concrete.
Fact is, if a question isn't about a specific platform, then its content is of interest to anyone on every platform. And you get to the part where some games exist on 4 or more platforms. This primarily came from re-releases, but nowadays there are a lot of games that release on the computer as well as on at least 2 of the major consoles. Genres aren't limited to a single instance, either. You have games like Allegience, which are part FPS and part RTS, or the myriad RPG-hybrids with platformers, action games, FPS, and shmups.
This all leads to filling up the tag set of a question very quickly. And, the key part is, almost all of those tags are going to be worthless for identifying the question to players of the game (which I reiterate is the essence of what a tag does). Our traffic, after all, is people looking for answers to the games they are playing, and the genre and platform of a general gameplay question is completely irrelevant to them. And if a game has a combined genre/platform count of 4 or more, then it completely loses the ability to have any other tags that would help those players filter their questions.
What you ultimately want is a way to be able to find questions about games that are in the genres you like. Adding tags to questions about that game, however, is a very ineffective process to that goal (due to the part where we lack the facilities to link tags with implications), and furthermore is a misuse of the tag system. Tagwise, it is simply redundant with the game tag itself.