As much as I love FIM, no.
Please don't do this.
Crossovers are for fan-works (some of which I love, don't get me wrong).
I have never seen a cross-over series succeed on TV, though, outside of things like The Justice League.
A spin-off might work, but I think it's still too early to even talk about it.
Let's focus on many more years with our current beloved ponies before trying to move on.

maybe Doctor Who, that would make sense considering he's kinda already in it XD