That’s interesting to consider.
For the laptops they could easily drop the Air, although it’s sort of their entry level device these days. The MacBook is their tiny offerings and again comes back to that “because we can” sort of marketing but with a huge price to match. Then there is the Pro in 13 or 15, not a huge amount to slim.
If I was forced to choose I would end up with two or three models in the range. You could drop all colour options and setting on space grey to maintain a brand identifier.
Lower the price point of the MacBook but keep the options for higher storage and RAM. This then becomes your entry level, it’s pretty, it’s tiny and lets Apple put the “Premium” experience in front of more people selling themselves as better than your usual Dell/HP machines.
Drop the 13" MacBook Pro, replacing it with an updated 13" MacBook Air.
Push the 15" MacBook Pro into a higher spec.
You would then have three pretty differentiated products at different price points. If push came to shove you could even drop the 13" completely, although I have no idea what their sales of 13" vs 15" Pros are.
On the desktop side there aren’t alot of options to being. Drop the 21". The rest is all internal config which could be simplified.
The only question then is if Apple are willing to either take a cut on the margins of the new low end model to maintain the same sort of entry point OR are willing to drive up the cost of that entry point. Sadly I think they are just fine with the latter.