There are rumors about a 15" Air and that would be interesting...but does not make sense to me. Too many laptops near that category; plus if there was a 15" Air, it would not have fans and would be heavy; why call it an "Air".
Ideally, I prefer a powerful Desktop (like a studio) and a powerful light laptop. But Apple seems to not want to do that, and always make you buy a few in their category (one does not have what the other has).
Keeps business and $ coming in. They could do this...but they want you to buy a mini and studio and Pro and Air and a studio display for different purposes.
I push my gear really hard and there isnt much the M1 cant do. Ye its not ideal for all tasks but considering the 2019 MacBook Pro took 20 mins to export a 10 min 4k clip and the m1 can do it in 7 mins and the pro can do it in 5 and the max in 4 we are reaching levels of diminishing returns.
Previously it was pointless buying a high end light laptop as they were so thermally constrained that the £3-400 chip upgrade made no difference as it would hit TDP really quickly. The 12" MacBook and the 13" air were both victims of this then they would also eat through the battery which made them really difficult to use. The base models were the obvious choices because the chassis couldn't deal with the processors. With Apple silicon this is much less of an issue and even the base models out perform the top end pro machines in most tasks which makes them 10X the performance of their equivalent predecessors.
The 15" light laptop absolutely makes sense as not everyone needs the high end specs of the 16" but may like the bigger screen as you can make it scale, say if you have less than perfect eyesight, more screen real estate. A lot of companies now won't offer a desktop for use, rather a laptop because of flexible working. Someone may have to go from having a pluggable desk set up at work with a display but may not at home so every inch counts.
Say you go from a 24-27" display at work but then have to go down to 13" at home it's a big difference, this is why many like the larger laptop. My work gives every employee 2x 24" displays as a base with a lockable set up.
The other key thing is the 16" starts at £2700 which is a huge amount of money if you're only wanting the larger screen over an entry point of £1200 with the 13" MacBook Air. Say it was £16-1800 it would fill a gap a lot of people find themselves and would be capable enough for 90% of people.
It's really funny how in the first gen of apple silicon the M1 was literally a game changer. My £5k MacBook Pro was loosing out in most cases to a £1500 MacBook Air. That level of power is unprecedented in terms of capability, in fact my £5k iMac spec 10 core i9 the m1 MacBook Air isnt far behind. The powerful chips are here they just need to make another ultra portable.