For example, http://stackoverflow.com/git~/latex/ could behave like a virtual SE which covers only questions tagged [tag:git~] and latex. The intersting/ignored part would be ignored for these tags, new questions would already (editable!) contain the tags (wildcards would require some drop-down-menu) by default. The link http://stackoverflow.com/latex/formatting/q/2812892 would be equivalent to Change paper size in the middle of a latex document?.
The benefit of this is, that all those proposals at Area 51 that are subsets of others, e.g. jquery < SO, StarCraft < ArQAde, could have a virtual SE for their specific tag, and still be part of the big, more general site. The virtual SE could even have it's own domain, if desired by its users. And by adding a subtle "generalize this SE" link, the real SE could also be reached.
edit Clarification: Yes, one can already use e.g. http://gaming.stackexchange.com/questions/tagged/starcraft-2, but there will always popup a Starcraft II proposal. But instead of opening another SE for that, you could just offer a virtual SE based on that tag and both sides (those who want one general site, and those who believe their subject is broad enough on its own) will be happy.