You don't need an arm processor, many modern x86 chips match or outcompete m series on power efficiency and performance. Mainly lunar lake gen 1 and the new gen 3 (arrow lake not really).
The efficiency of arm chips was never arm, really, it was the manufacturing node and SOC design. Well, Intel and AMD can make SOCs, and they do.
There are reasons beyond pure power efficiency to use ARM processors. It is a nice architecture to work with, especially if you plan to write low-level code. Also, you might want to deploy on ARM servers.
Also, there is the question who in general makes Laptops as nice as a MB Air? Who makes a fan less laptop of roughly comparable power?
If you're writing true low-level code then you're most likely doing it for performance reasons, like ffmpeg. But ARM doesn't have the instruction set to make the best use of that, x86 does with its extensions. Otherwise, the compiler handles translation, so there's just no reason for you to care about the assembly unless you're writing assembly.
As for nice laptops, I think Asus and Lenovo makes some nice ones. I don't believe any are fanless, but most are quiet - Lunar Lake gen 3 is an SOC with a base TDP of 25 watts, and it can even go down to 15 watts. These CPUs are slightly faster in multi-core performance than M4, and they use similar wattage. I believe the Asus zenbook duo gets better battery life by a wide margin because of the 99 watt-hour battery. They still fall a little short of M5 in performance, but it's very close.
As for servers, it's a good point. But I think currently most servers are still using x86 CPUs, so it might not be relevant for a while.
ARM servers definitely seem to get more popular. Seems that for a lot of tasks they are the more economic option. Consequently, you want more and more development for ARM. That would be one reason. The other is, that developing for ARM is more fun, whenever you touch parts which are architecture-dependent.
For the computer: the Air is a great laptop. I am very happy it doesn't have a fan, so it can never get a clogged fan and it works great. Currently, I am running Linux on it via VMWare, so I get the best of two worlds. And Linux really flies on it. Once it is no longer supported by macOS, I am certainly going to go native Linux. As it is an M2, that probably would work already today.
If you want an ARM CPU, there are now a few single-board computers with a quadruple Cortex-A78 CPU in the "Qualcomm Dragonwing QCM6490" SoC (similar to a Snapdragon from the flagships of 2021), which run circles around Raspberry Pi and the like.
There are also older NVIDIA Orin SBCs with Cortex-A78, but those are severely overpriced, so they are not worthwhile, unless you really want to use them in an automotive project.
For software development, the Arm-designed cores have the advantage of excellent documentation, unlike the proprietary cores designed by Apple and Qualcomm, which are almost undocumented. Good documentation simplifies software debugging and tuning.
Unfortunately there are no cheap solutions for developing on the latest ARM ISA variants (except for a Chinese Armv9.2-A CPU, which has some quirks and is available in mini-ITX and smaller formats). For the latest ISA, you should develop software on a smartphone, e.g. on one of the Motorola smartphones that have DisplayPort for connecting an external monitor and a desktop mode for Android.
The Qualcomm laptops have various problems with Linux that have not been solved yet.
You have much better Linux support for an older Snapdragon from 2021 (with quadruple Cortex-A78 cores) which has been rebranded as "Dragonwing QCM6490" and which is sold by Qualcomm for use in embedded computers. Thus Qualcomm promises at least 10 years of support for it.
There are a few cheap single-board computers with it, e.g. Particle Tachyon 5G and Radxa Dragon Q6A.
Unfortunately, "cheap" means something very different today than last summer, due to the huge increase in the price of DRAM. Nevertheless, the SBCs with soldered LPDDR memory have been affected less by the price increase than the computers for which you have to buy SODIMM or DIMM memory modules, which may cost now more than a mini-PC in which you would want to install them.
Nothing seems to be close to the MB Air. I would definitely be interested in buying a comparable hardware, if Linux is better supported than on the Air.
