in terms of normally produced models, 20x24 seems to be the outer limit, if that is the original question.
Basically. Not that any ever come onto the E-Bay market. I've been able to collect well up to 12x15 plate cameras and accessories, that seems to be the current outer limit. Not being a museaum and having used up my space, that is my limit. It is nice to know that my gear is in the middle of the range of sizes. Always something to look forward to. That undiscovered long lost huge camera outfit may yet exist in some lonely barn or old attic waiting to be discovered.