Today I experimented with NAT64 / NAT46 a bit.
The Setup to test this is relatively easy:

I took 2 Windows-Servers (2008R2), one with only IPv4 and one with only IPv6.
The 2 SRX’es are dual-stack capable and have a transfer-subnet (IPv4) between them.

Test-Scenario: Serverv4 pings Serverv6’s “v4-Address”, which is actually a “Proxy-Address” on the SRX and gets the reply – without requiring the v6-Server to have an IPv4-Address. Reverse should be the same: The v6-Server pings a v6-Address but in the Background it is the v4-only Server that replies. This worked very nice and I hope to see more of that in the Future at the customers sites – and I bet I will since IPv6 gains more and more attraction here in Germany 😉