I'm expecting two 24" iMacs: an entry level M1 and a top-end M1X (or possibly M2).
The M1 model will be a cross between a Macbook Air and a Mac Mini in ports and performance. It will probably be 4K since the Air is now also retina... or maybe not.
The M1X will be 4K, have 8GB RAM standard (upgradable to 32GB), support two external displays up to 6K, and have about the same ports as the 2019 Intel models did, except with USB4 support. 12 CPU cores (8 power, 4 efficiency) with 16GPU cores seems like a good guess.
A 6K 32" iMac with the M1X that replaces the entry and mid 5K Radeon Pro 5300 models is plausible but unlikely. The i7/i9 Intel 5K iMac will certainly continue to be the top-end until late 2021 when apple will announce an M2/M2X chipset.