Things don't evolve if there isn't a reason to evolve.
Eevee is already perfectly suitable to it's environment so it doesn't have to evolve.
It would only evolve if the environment changes.
Besides I think Eevee is already the product of an house living environment.
toxeon and Spireon are both the names of my fangame's eeveelutions >_>
Plenty of pokemon evolve for no reason a all.
Hate to rain on your parade, but technically Eevee could get another normal type evolution. It could be "upgraded" in a similar fashion to Porygon. Enter a new gene to Eevee's already unstable DNA and it could mutate further without a new environment, so it wouldn't change type (except perhaps become Steel?).
Porygon isn't Eevee - it doesn't evolve to adapt to its surroundings. Unless they change everything about Eevee, there won't be a normal evolution. As we've seen so far, you can't just "enter a new gene" into Eevee. I wouldn't mind seeing a normal type evolution of Eevee, but it will not happen because it wouldn't make any sense whatsoever, and isn't needed.
"Technically" anything can happen to a pokemon. Eevee could suddenly have its sprite redone in the next generation and look like a rat instead - could this happen? Technically, it could, but clearly it won't. This is the same case for Eevee and a normal evolution. The first example is a little extreme, but I'm pretty sure you get my point. :p