Hybrid Races

I've been working on the Character Creation chapter of my "house system" and I've gotten to the point where I want to make a decision about whether or not beings from different species can mate and therefore determine if I need to write any rules to govern such beings without having to write a million and one hybrid races individually. In the case of the Asari, the answer is a resounding "yes", but they don't necessarily need to mate in conventional sense to produce offspring and all young born from mating with an Asari are Asari in most every discernible way. Star Trek gives many examples of different species that can produce offspring: Humans and Betazoids, Humans and Klingons, Bajorans and Cardassians, and so on. Such pairings are also found in other series like Farscape (although Humans and Sebaceans are so similar genetically that it doesn't stretch the imagination too far) and Star Wars. Plus, since this setting is very much in the space opera vein as opposed to trying for a more hard sci-fi angle, it's not too far out of the norm to draw upon fantasy ideas like the half-elf, half-giant, and the like.

I'm inclined to allow such beings as supported in the setting, and I think I have a decent idea of a relatively easy way to handle these beings. However, there would have to be limits like only near-human species would be genetically compatible enough for such pairings. So there wouldn't be any Dralasite/Vulcans running around. Species that are decidedly more insectoid (Verpine), animalistic (Wookiee), or just weird (Founders, Dhamrin) simply wouldn't be allowed except as some GM plot device. After all, who am I to say that some Gene-Splicer couldn't create some sort of hoary abomination to unleash upon an unsuspecting galaxy?) I'm thinking of adding in a section to the species details that states whether or not they are genetically compatible with other species, much like what I'm doing to state whether or not a species can have psionic abilities, has a sufficiently malleable genetic structure for mutations, or has a physiology incompatible for cybernetics. Sex isn't typically something that I cover in my games (the times that the "brown-chicken, brown-cow" has occurred, it's all happened "off camera") and it's a subject that can make some people squeamish for a variety of reasons, so I'd like to handle the issue as gently as possible without tip-toeing around it like I'm writing for a pre-pubescent audience that giggles as the merest mention of anything slightly adult in nature. I'm not sure if I'll end up adding such an entry to the background information for each species, but in light of possibly (well, very likely) adding of the hybrid races rules it makes sense. 

So I put the question to you, loyal reader of this rather haphazard blog, would such rules be a turn-off to a game even with the knowledge that the campaign is decidedly sci-fantasy (and even possibly a bit "gonzo" in spots) or would it still feel alright and keeping in the spirit even if the idea of different species mating and creating offspring is scientifically ridiculous? 

There are also other species in the galaxy that can mate with other species similar to the Asari parthenogenesis or by means of genetic manipulation. The Satyrix (of Iron Kingdom fame) can mate with humans and other near-humans thanks to changes made to their genetic make-up to make up for the fact that they simply do not bear enough males in their society. The Valkyria (from the Savage Worlds setting, Slipstream) can mate with certain other species as well that are similar enough to their own genetic make-up. Therefore, there are instances beyond the Asari where other such beings can mate with others, but in each case the offspring is almost always the same as the mother. 

Anyway, that's what I was working on at the moment and decided that I'd write about it. Any thoughts?