Special:Nearby, isn't really a good substitute because it is a simple list of pages with no way to filter them, or indeed even sort them in any manner whatsoever. In any case, even if goal is to help people remember the keywords, there's neartitle: as well, and that's simple enough to be memorized, much like "intitle" or potentially even "boost-neartitle:" (favour items near this page). It would probably work exactly like "intitle", heck developers could easily just change the keyword "intitle" to "neartitle" and most of their work would be done.
Also, the argument seems slightly counter intuitive. If something has few cases of being typed, then it is a greater reason to implement an intuitive user interface, Extension:Cirrussearch could theoretically support a simpler "nearby:yes" keyword but there is simply no valid reason why it would ever support that when it can and should be provided by the user interface in the form of coordinates (e.g. "coord:xxx, xxx").