As has been said before, most of the issues baring half-breeds from being common (whether different races or just different clans) is the cultural differences. Miqo'te alone have quite stark differences between the two clans: social structure of their tribes (when they are tribal--there are plenty who aren't as is evident in game now), settlement locations (Seekers are partial to Limsa and the Sagolii, Keepers are mostly in Gridania and the Shroud), and even basic things like being nocturnal vs. diurnal. This makes half-breeds unlikely.
Of course, anything unlikely/rare is bound to be quite common amongst RPers! My own character fell in love with a Hyur. But she was raised non-tribally, around Hyurs for the most part, so it makes sense that she would be attracted to them. There are always ways to wiggle and make things work.
My own opinion on half-breeds of any sort has always been that they would take the main traits from one parent. That is, a Hyur and Miqo'te couple could have a Hyur or a Miqo'te child, not a mixture of the two, and when instances of combining clans occur they'd appear as a Seeker or a Keeper. That sort of thing. That's just based on the lack of mixing of traits that I've seen in game (except for that silly Seeker in trailers who has Keeper markings due to SE changing their mind on something and not being able to adjust her appearance because the CS was too far in development xD). But it obviously DOES happen sometimes: F'lhaminn is a Keeper of the Moon by all appearances (skin tone, eyes, fangs), but has a Seeker of the Sun name.
Of course, anything unlikely/rare is bound to be quite common amongst RPers! My own character fell in love with a Hyur. But she was raised non-tribally, around Hyurs for the most part, so it makes sense that she would be attracted to them. There are always ways to wiggle and make things work.
My own opinion on half-breeds of any sort has always been that they would take the main traits from one parent. That is, a Hyur and Miqo'te couple could have a Hyur or a Miqo'te child, not a mixture of the two, and when instances of combining clans occur they'd appear as a Seeker or a Keeper. That sort of thing. That's just based on the lack of mixing of traits that I've seen in game (except for that silly Seeker in trailers who has Keeper markings due to SE changing their mind on something and not being able to adjust her appearance because the CS was too far in development xD). But it obviously DOES happen sometimes: F'lhaminn is a Keeper of the Moon by all appearances (skin tone, eyes, fangs), but has a Seeker of the Sun name.