So unless your application contains a full DNS resolver that can walk the roots itself, you are relying on the DNS server from your provider to provide you with DNSSEC validated results. In this case the provider can simply return results without any of the DNSSEC results and things will be more than happy to continue on.
XLAT464 is not some sort of panacea, and requires a bunch of extra software running on the device to properly function. NAT64 with DNS64 means you ignore all of that, and only the provider has to know that translation is happening, from a device perspective it looks like it is running on top of a IPv6 only network with all endpoints only being IPv6. It's simpler, and maybe just the push providers need to roll out IPv6 more aggressively.