Anduin is King now, so he needs a lover. Let's look at his options.
Caila - Too old
Tess Greymane - Too old
Venessa Vancleef - Too crazy
Therefore the only suitable choice left is Wrathion. Age isn't a problem because he's a dragon, and he's one of the only people Anduin has actually had meaningful interaction with.
And as for offspring? They could get a surrogate. Jaina should do nicely.