It's not nonsense. Since the beginning of Arda, how many elven-human unions were there? Four, if I'm not mistaken. Two in the First Age (Beren and Luthien & Tuor and Idril Celebrindal), one in the Second (Imrazor and Mithrellas) and the last one between Aragon and Arwen.
Over more than eleven thousand years of history, there were FOUR. That's why we deal with Aragorn's marriage through events instead of the game's marriage mechanics: such unions are too special and rare to be allowed to happen on a daily basis (yes, I'm exaggerating here xD).
So, unless you guys can come up with really, really good ideas for events that could allow the player the possibility of having of such union, I don't think this "policy" of ours will change in the future...