I think any sort of split-horizon on devices you don't fully control is going to start giving you a lot of problems going forward. For example, any sort of DNS

I think any sort of split-horizon on devices you don't fully control is going to start giving you a lot of problems going forward. For example, any sort of DNS-over-https is going to make split-horizon non existent unless you control the client device. And presumably if you control the client to change the DNS behaviour, you could turn off this new behaviour too. Fwiw, I think this is generally good. Network operators shouldn't be able to arbitrarily intercept traffic on their networks.