Firstly if you are broadly familiar with their product line then you'd know that the Macbook doesn't remotely replace the Air.
As a regular user off the Air and those around me; all of whom use Airs except for like 2 people who need the Pro's big GPU haven't upgraded for four big reasons.
1. The screen resolution and quality.
2. Removal of the magnetic locking port and other port related issues that are well noted
3. Not enough RAM
4. Price
4b. If they use the Butterfly keyboard on the Air then that would become an issue as well.
Magnetic power port: This is huge and how ironic that MS launched a magnetic 'super' port for their Surface equipment and Mac moved away. I haven't had a Mac hit the floor in 10 years for the very reason this port exists
Mac Airs were more expensive when they initially launched, but afterwards they moderated for much of their time int he $1200-$1500 USD range. This is way way less than what's on offer from a Macbook.
Lastly, regarding the Macbook itself, the screen size is too small. This is a toy for a more niche use case. The Air is a mobile warriors tool box; it's got ports, longevity and it's just about impossible to break. What people don't often even realize is that the the triangular shape of the Air is a critical structural feature that makes typing easier than most others and also makes it impervious to nearly any reasonable drop. I've got so many dings, gouges and scars from it's heavy usage that I'm always amazed.
I genuinely would buy a brand new Air if it was 13", Retina which is so standard now, under $1500 and had 8GB of RAM. This is a completely reasonable expectation. What I would ask for is different. If I could ask I'd want a 14" screen, Retina, option of 8-16GB of RAM and a magnetic port. Two of those things you are know aren't going to happen, but I dream of day when the magnetic port comes back to me; life was much less stressful never having to worry about a $1000 devices safety.