Split horizon would point you at the same data center, rather than the writeable one. So that's more of a .local than a .internal. We discussed this, but ultimately the AD version we're on (pre-2016 Geo-DNS) it's not actually supported the way you'd need, and it's a nightmare to debug.

We'd consider it for a .local, when the support it properly there in 2016. Even subnet prioritization is busted internally, so that's a bit of an issue. Evidently no one tried to use a wildcard with dual records on 2 subnets before (we prioritize the /16, which is a data center) and it's totally busted. Microsoft has simply said this isn't supported and won't be fixed. A records work, unless they're a wildcard. So specifically, the <star>.stackexchange.com record which we mirror internally at <star>.stackexchange.com.internal for that IP set is particularly problematic.

TL;DR: Microsoft AD DNS is busted and they have no intention of fixing it. It's not worth it to try and work around it.