I'd be interested to know what you find as far as what Qos levels work.
Have you tried changing topics in your mqtt message program?
That's something I keep meaning to do. Dynamically changing topic.
Have one topic that is always listened to, like "home/SetTopic - home/furnace/temperature".
When it receives that it will subscribe to "home/furnace/temperature" and start displaying those messages.
I've got a bunch of those 8x8 LED matrixes with the 7219 chip on the way from China.
Planning to build a big scrolling text display and make that a mqtt message displayer. There are a lot of things that come to mind as far as controlling that via mqtt aside from the dynamic topic(s). I don't know what's Arduino specific and what will port over easily to ESP, but I've seen some neat projects where you can set all kinds of scrolling options, speeds, etc.