Most mobile clients you're going to get your search and browsing through OPDS - so a library and a search function, but no tag support. Just (afaik) author, title, publisher, year, etc.
So that kind of fuzzy sorting is, at best, limited to the web interface for servers that support it (like Kavita). Which means browsing in almost any context native to a reader device/app is not going to support tagging.
If that changes, then sure, it could be plenty useful as a single giant list with neatly browsable tags. As of what's out there now and usable (again, afaik) it is not.