The M1 is the first iPad SoC to be used in their consumer laptop/desktop models - I'm not particularly shocked it only supports 2 displays. It was never meant to and didn't replace serious rendering workstations with high core counts and dedicated GPUs.
As you say hopefully the next models can expand into that space but I'm not bewildered it didn't go from iPad to replacing rendering workstations with 3 displays in one generation. After all if you still want a MacBook with more than 16 GB of RAM they'll still sell you an Intel model anyways.
It's not surprising the M1 isn't great when it comes to external displays, but it's a little disappointing that Apple puts it in a laptop with such "Pro" branding and price.
As you say hopefully the next models can expand into that space but I'm not bewildered it didn't go from iPad to replacing rendering workstations with 3 displays in one generation. After all if you still want a MacBook with more than 16 GB of RAM they'll still sell you an Intel model anyways.