Yeah, currently the only detection that happens is OS version, and just 
so we can block (or at least log) users who are trying to install on 
supported versions. The install directories are unconditional.

Any dynamic detection code would have to go into 
Tools/msi/bundle/bootstrap/PythonBootstrapperApplication.cpp and would 
update variables defined in Tools/msi/bundle/bundle.wxs. If you find the 
code for getting the ProgramFiles(Arm) directory, you'll see an example 
(which is probably the right one to update to handle the range of 
platforms).

However, I think we should consider the 32/64-bit install directory 
names to be a compatibility concern, and shouldn't modify them generally 
out of some kind of sense of "fairness". If it's trivial and safe to 
detect 64-bit running on ARM64 (which, as you say, it ought to be), then 
we can update its directory name there by default.

We should probably also display a notice in the installer when 
installing the Intel builds on ARM. The 64-bit version is fine, but the 
32-bit version has issues, and my experience so far is that the native 
build is significantly faster than both. We can do that another time though.