I have done a test setup of IPv6 on NAT using ASA5545(9.1.1). I am NATing external IPv6 to a pool of IPv4 and internal IPv4 to public IPv6 using static NAT.
The basic connectivity is established and workng fine. We would be checking the application response also on the same.
Need input from the experts on performance and challenges if any.
Not implemented something like that before but I can anticipate some issues with MTU since you are targetting appplication services.
Usually in IPv4 MTU is handled (fragmented) by the routers but in IPv6 MTU is decided by the end client who is generating the packet with the help of PMTUD and it will send only MTU size which is maximum on the segment. So to make it simple-> Your application (IPv4) might expect a router to do the MTU fragmentation but IPv6 device will expect your end device do to a fragmentation.