I'm sort of in that boat now. I've got 2 bp's, a brazilian rainbow boa and I only have room for one more snake. I have no plans of moving anytime soon, so I'm unfortunately at my limit. I just can't decide what my last snake should be.
Right now I'm stuck between a female BEL, a pewter corn (couldn't get that until next breeding season), a Hog Island boa, Woma python (if I can find a docile one, they are soo beautiful!) or a docile children's/spotted python.
So, I'm curious... if you could only have one more snake, what would your last be??