A 3rd party could produce a complete PC on an MPX module.
You can put a complete PC on a USB stick.
Seriously though, I think the era of dual boot is over. It would require insane engineering to accommodate a dual platform ARM/Intel hardware thing. How do you share buses, memory, timing, T2 chip, etc etc without compromising one or the other or have constant crashing? The cost would be enormous.
It would probably never be truly compatible with all PC software, either.
A decent PC can be had dirt cheap if all you need is occasional Windows access.
If you really need a powerful Windows workstation, or a gaming rig, then you're probably building your own, or buying something like an HP Z series.
Increasingly, you may not even really be working on a desktop but in a hosted VM in the cloud somewhere, or accessing your work PC via Microsoft Remote Desktop. Or your tools are all web-based or cross-platform anyway.
I think all the trends point to a greatly decreased demand for dual-boot. Is it convenient and cool? Sure, but think about the trade-offs from Apple's point of view.
Dual booters (talking pros, excluding enthusiasts) are a shrinking slice of the market, and the cost to support them probably does not make sense anymore.
By retaining Intel / x86 hardware, it hobbles their ability to make a clean transition to a new architecture. For laptops, it means stlll dealing with hot, power-hungry Core chips, vs being able to get the big compute-power-per-watt / battery life boost that the A-series platform will give them.
It's not like 2006, when Apple was trying to cement its decade of recovery from where they were in 1996. Maybe they needed to tout Windows compatibility as a way to lure corporate buyers back, but now that macOS / iOS is 20 years old, IT departments are increasingly flexible about giving you a choice of machine. In many cases iOS is even preferable because of its locked-down nature (when developing and distributing corporate apps using managed devices).