I’ll be the unpopular one and say this is a weird prediction. A 15” MBA has no niche when the 14”MBP and 16”MBP exist.
It is more about price market segmentation than 'niche'.
If Apple raises the MPB 14" price a bit and places the MBA 15" in the middle between MBA 13" and MBP 14" there is room if that price range is wide enough.
Apple could simply just dump the lowest end 'binned' Mx Pro option from the MBP 14" line up. Just start at the full CPU core count M2 Pro and just walk a GPU core binning ladder for options. That is another $200 bump over the gap that exists now. That would lower the fratricide between the MBA 15" and MBP 14".
[Similar issue with MBP 16" . trim off 512TB SSD for customers who were really way out of their price range but just primarily trying to grab a larger screen. The binned down M1 Pro is already completely trimmed off in the 16" line up. ]
The MBP 14" won't be close at all in either CPU or GPU performance. The folks who want to buy performance get the 14" and the folks just looking for a larger screen on a basic laptop get the MBA 15".
Apple should push the M2 Pro into something like a Mini (and perhaps larger screen iMac) to keep the number of M2 Pro SoC packages sold at a higher rate. If they actually really needed a place to 'dump' binned CPU cores M2 Pro packages could just to that outside the laptop line up.
MBAs are all about portability. I could understand a thinner lighter 13”MBA, but a 15” one? Nah
The path to lighter is with lower battery consumption. If stick with lower power consuming M2 in the MBA 15" and far less brighter (and lower refresh ) screen, then they don't need quite as much battery. No fans ... lighter and lower battery consumption. If battery is thinner, then case is thinner. If case is made of aviation aluminum and thinner .... then it is also less weight of the enclosure. No SD reader, no HDMI port ... lighter. Relatively smaller speakers .. lighter.
The slippery slope is if that the larger screen's frame is still rigid if trim more metal out of it.
MBA 2015 2.96 lbs ( 1.35kg )
MBA 2018 2.75 lbs ( 1. 25kg )
MBA 2022 2.7 lbs (1.24 kg )
Apple has pretty much 'milked' the 13" air enclosure about as far as they are going to go. ( without dumping aluminum. )
If Apple got the MBA 15" to the 3-3.1 lbs range it would be approximately just as thin and light as the MBA 2015 was. However, it would have a larger screen. That actually would be a challenge that probably deserves having an 'Air' adjective thrown at it.
If it ends up being just 0.1 lbs lighter than a MBP 14" ( 3.4 versus 3.5 lbs ) , then not so much. If they can chop 0.5 lbs, then that would be substantive lighter.
The bigger problem child Apple probably ends up with is not the MBP 14" versus MBP 15 , but with the MBP 13" M2 that is just iterating with the old style case at 3.0 lbs. Bigger case size for the MBA 15" probably means it can passively deal with some thermal issues better than the old MBP 13" enclosure can ( very likely much better than the regular MBA 13 can). It would weight about the same with a bigger screen.
Apple swapping out the MBP 13" from the line up for a MBA 15" would be a decent clean up. If user don't want a thermal throttle plain M2 ... go bigger screen. ( if pushing the M2 hard doing lots of video editing or heavy compute then the bigger screen is often helpful also ). The MBP line up starts at Mx Pro and goes up (no 'plain' Mx options).
Spread them out price wise so incrementally lower fratricide and it should work better.
[ P.S. that could be a long term 'swap out' for the MBP 13 M2. Apple could keep it 'drifting' in the line up for a couple of years for those you happen to like the touch bar option. It is old parts from Intel era so could keep a low volume manufacturing line going for a while at lower prices for a niche as that fades out. When the MBA 13"/15" move on to M3 ... Apple just sells old stuff for MBP 13" if a minimum number keep buying it. ]