So the original quote was:
Having higher pixel densities just reduces ISO performance.
Now pixel densities have been increasing for years. And yet high ISO hasn't got worse (has it?). Clearly there is more going on here. "It's physics" isn't good enough, sorry. I think Privatebydesign's point of comparing like with like is relevant - especially as each generation of cameras has managed to increase pixel counts *and* high ISO performance (as a general trend, I guess there will be exceptions). So when we are discussing a future camera, which presumably has a more modern sensor than past models, why should we not expect this trend to continue?
Otherwise, those seeking the best low light performance would always use the oldest, lowest-resolution sensors.
I'm just trying to understand reality, I don't have an axe to grind. Surely something as seemingly basic as this can be settled objectively one way or another?