It'll definitely be a different chip either way. To have a 2x or 4x M1s would require interconnects between the CPUs for sharing RAM and general communication, which isn't there on the M1 currently. So at a minimum you're talking a rev of M1 to add such interconnects. But that all seems very unlikely. If they do go that route it'd almost certainly be something like AMD's chiplets instead of just straight "multi-socket"