Currently, nothing offical has been released. In the portuguese foruns is frequent that question. Actually, by what's know, we can only speculate. However, three things are clear:
a) compared with the original AIM-7, the improved ESSM can give has more effectiveness in the interception of missiles and, because of that, in air defence missions.
b) Portugal always searched for two air defence frigates; the Karel Doorman are, in fact, multi-role vessels; adding to this fact the construction of a LPD ship, it's clear that Portugal must adquire some capabilities on this area.
d) the Mk29 launcher of the Vasco da Gama class and the Mk48 from the Karel Doorman class, as well as the radar systems, can fire and guide the ESSM.
But, as you know, the use of the ESSM with the current ships' sensors is limited. So, I would advance with this hypothesis: the introduction of the ESSM will only happen after the modernization of the Vasco da Gama class and probably will envolve the substitution of the radar system. In any case, the Vasco da Gama class is, presently, well fitted for ASW missions, so it's questionable if the portuguese Navy would transform it on a dedicated AAW ship.
I hope that I've been clear - sorry for my english
.
All the best,
Pedro Monteiro