I was just thinking that Line 6 is going to want to share their IP across a family of products like others do (including Line 6). Stadium XL and Stadium "standard" are just the flagship models. I fully expect them to continue to fill out their product lineup with Stadium class processing and features ..... and sadly, to quit developing on the older Helix line completely.
So the question really comes down to what the Line 6 product lineup looks like. I would say that the current HX Stomp XL is the head to head competitor to AM4. I also don't think that the HX Stomp line will be getting much new development while Line 6 fills out their new Stadium based product lineup.
That is just how I read the tea leaves
Also, Line 6 seems to undercut Fractal in price. I expect that this will continue in the future so the max I could see the SM4 sell at would be $600 to undercut the AM4's $700 price. Line 6 can do this due to higher volume (and arguably better hardware engineering designed specifically for high volume manufacturing low costs).