So I am working on replacing the floor in an upstairs bathroom in a ~100 year old house. The 4 layers of flooring I removed were hiding the original hardwood floors, which were garbage to start with. Leaking from the toilet had rotted much of the flooring around the toilet, which has now been removed to expose the (probably original) pine plank subfloor, complete with large gaps and holes. I have considered pulling out the subfloor and replacing with 3/4" or 5/8" plywood in order to create a stable base for tile, but ran into a snag. Whoever plumbed the bathroom evidently got off on the whole measurement thing, because the edge of the hub on one of the joints in the toilet waste pipe actually penetrates through a hole they cut in the subfloor. Not a lot, but it is definitely proud of the subfloor surface. Since all of the DWV is lovely cast iron, I'm not sure that dropping the pipe down below the subfloor is an option.
Given that I wanted to install tile, do I have any options? Is it kosher to just build up the subfloor until it is above the hub, notching the bottom of the new subfloor surface to fit over the protruding hub edge? Also, the joists in this house are 24" apart. Assuming I can get this hub protrusion issue sorted, am I going to need to install stringers throughout in order to get the rigidity needed for tile?