Maybe I haven't had enough coffee but why would anyone want elite qualification levels to be measure in stays instead of nights?

The maximum stay:night ratio is 1:1
....but if you have a 3 night stay, you are now getting 1 stay instead of 3 nights, so 33% of what you'd be credited for a night-based system.

I guess if the suggestion here is that Marriott should change to a stay based system --and-- readjust the requirements (say from 75 nights for PLAT to 25 stays), then I guess it could be a good thing but under that circumstance a beneficial change would mean more PLATs and that's certainly something I wouldn't want to see.