Will any of these (including MAP-E) support such nasty (in terms of
burying IP addresses in data payloads) protocols as FTP and SIP/SDP?
I'm a fan of these solutions that (only) use NAT44 in the CPE as this is exactly what they're currently doing, and the CPE vendors have already "solved" the problem of application support (SIP, FTP etc.) at least as far as the end-user is concerned.
It seems that introducing an extra layer of NAT at the ISP for NAT444 is creating a range of new problems, not least being scalability. Big CGNAT boxes are expensive.
Aled