SE did confirm/canon that the races -can- have "mixed" kids.
My only beef with that is, how do you make a half Lala, half anything else?

@ Ramira; Hyurs, Elezen and Miqo'te are that alike to you?
I find Roegadyns more closely resemble Hyurs and Elezen than Miqo'te do.
(Highlanders are about the size/build to be mistaken as Roegadyns, and this can be used derivatively among Midlanders... or other races...?)
It's the (shape and location of) ears and the tail that I don't think Miqo'te are that genetically close to any other race.
Between Hyurs, Elezen and Roegadyns, there's just the body size, some portion differences, and the pointy/roundy-ness of the ears.
(Everything in this post is IMO, and just my 'two cents'.)

Silly thought here...
Lalafells maybe evolved from Meerkats or hamsters?