I might be wrong but it seems the point of the TTIP is to say "Ok our norms are equivalent in the US and EU, so a US car does not need to pass EuroNCAP to be sold in Europe"
Or rather we would align EuroNCAP on less demanding american norms, which would have the same result. A five star EuroNCAP post-TTIP would not be equivalent to a 5 star pre-TTIP.
EuroNCAP isn't a regulatory thing, and it isn't mandatory, it's basically just publicly fundded consumer information. Even if more models are allowed to be sold because they pass new "harmoinized" (read: relaxed) safety regulations after TTIP, they won't sell unless they score high on NCAP. (Specialty models like pickups, performance cars likely not that sensitive, but regular passenger cars and SUV's definitely would sell poorly without a high NCAP score). A US manufacturer knows this.
I don't think (at least I hope) that NCAP would ever relax their testing procedures. Rather, they make it stricter every year, as they should.
Or rather we would align EuroNCAP on less demanding american norms, which would have the same result. A five star EuroNCAP post-TTIP would not be equivalent to a 5 star pre-TTIP.