I haven't heard of a game that needs such a thing, but that doesn't mean it's not worth submitting.
Relative Searching is based on the same concept: you know the order of the characters but not the offset where it starts counting them. But that the offset changes around within the game is slightly different. Not related to this tool. but have you thought further about re-inserting your text? How do you determine which table offset to use for writing later? It seems to me like you'll have to figure out why the offsets change before you can do anything with the text dump. And then this searching method will probably not be needed anymore. I'm not saying your tool is the wrong approach, it just seems like there is a key piece missing that it would even be needed.
The GB/C hardware is one of the simplest and easiest systems to hack out there. If you're trying to build a table, all you have to do is look at VRAM and see if it stores the entire font there. If not, you can easily debug to find where the text is loaded by setting VRAM breakpoints etc. It really only takes a few minutes to do as the debugging capabilities are quite advanced for the GB/C.
My honest opinion here, but I feel like a case study on how to find text encoding/locations etc by debugging would be more useful than the tool as that is the ideal method to do all this stuff. I stopped searching for text in a hex editor when I learned how to debug and reverse-engineer games.
My personal opinions aside, there's probably some use to it for beginners though.
More open source tools are nice to see.
That said other than your workflow perhaps being more obvious/slightly less esoteric and the easier replace/alteration options what is all that different to the wildcards being supported in something like http://www.romhacking.net/utilities/513/ ?
Honestly, using a standard table file will probably be more utilized by the community than some new XML format. We've only just managed to get some consensus hashed out on table formats. The hope is that new tools will implement that consensus, and not propagate further incompatible formats.