In my view the M1X will be a slightly more powerful M1. Perhaps simply an over clocked M1. I do not expect a complete new architecture for the 24 inch iMac, but I expect it will cost close to 1000$. They should use it a cheap gateway to services just like the MacBook Air is.It would be nice but I doubt the new model is already on the way. I feel like Apple is going to drag this out across 2021 as everyone waits for their machine to be updated to Apple Silicon.
I think most people assume the iMac is going to make use of an M1X or newer chip, but I would not be surprised if the entry level iMac is replaced with the current M1.