The end users of these domains are globally distributed and served from 14 different data centre locations across the world.
To do the geo IP matching we tried a lot of things, third party services etc but couldn't find one that works well and are priced well.
For example, the hosted DNS service we use also have a IP based filter chain feature but are priced around $22 per domain per month as add-on.
At the end, we built a anycast based solution that was very painful to setup but works fine now and can use a single A record that works across the world. We had a get a ASN, a /24 block and hell lot of back n forth with a government run org to set it up.
A "hosted" scriptable DNS server which takes the location as input and output IP of nearest edge server as output is the exact thing I needed. So yes there is definitely a niche market for it.
I still have to explore and see how closely bunnydns is able to get the source IP/location (tricky) and how does health check etc could work but definitely something I would explore and consider.