As of a change made yesterday, the speedrun tag's usage guidance states one should "Use this tag for questions about speedrunning in general - if your question is game-specific, please use the game's tag instead." However, of the 17 questions that still have the tag, only 4 actually follow this direction - one of which is closed as Too Broad, and the others could potentially be considered such as well. There's a reason for this: very little in speedrunning is game-independent, with every game tending to have differences in the rules of speedrunning them. Things can even vary widely within a single game depending on the type of run being done.
In particular, there are at least a few situations where I believe the speedrun tag would apply to a game-specific question. Conveniently, I can find at least one existing question for each of the topics.
When "fastest" and "best" aren't necessarily the same
In a speedrun, one obviously wants to complete the necessary tasks as fast as possible. However, this often doesn't coincide with the easiest or most efficient way to do something. Maybe you need to go into a difficult area while underequipped, maybe you need to use a lot of a limited resource, but whatever the case, you're looking for a tactic that you would primarily only use if you're trying to go fast. While one could argue that a person could choose to do such things as a challenge instead, that could largely be applied to anything, and I'd expect the most common use of the information to be more significant when it comes to determining tagging.
Potentially a subset of the above, but it seems sufficiently different that I'll make a separate point for it. When one has options and needs to determine which one would be the fastest to take. As above, it's not necessarily the easiest or most efficient choice, and "routing" in this sense is rarely relevant outside of a speedrun (or imitating a speedrun more slowly).
Seemingly the most obvious category of game-specific question that the speedrun tag would apply to, questions directly relating to speedruns of a particular game, including allowed versions and category rules. (It seems questionable whether this particular category of question is actually valid for our site, but the example question seems to have avoided an attempt to close it, which is currently providing the only precedence I'm aware of.)
As a further note, while a speedrunner of one game is only marginally more capable of answering speedrunning questions for other games, many such questions require knowledge specific to those who have an expertise in speedrunning that particular game, or otherwise have specifically studied speedrunning the game. i.e. "speedrunning Super Metroid" (to use a particularly popular example) is a distinct skill set. Most non-speedrunning Super Metroid players won't be particularly proficient at answering such a question, nor would a non-Super Metroid playing speedrunner (though either of those groups would have a better chance of answering than someone who is in neither group). But requiring a theoretical new super-metroid-speedrun tag for such expertise, plus another for every other game-specific speedrunning question, would quickly get out of hand, especially when we can simply use both more-general tags.
With this in mind, does the new intention that the speedrun tag be restricted to game-independent questions really make sense?