Hybrids....
Joking aside, I'm not opposed to the idea, though EgonVM covers the practical reasons why Hybrids are an issue. The multiple forms and the conflicting needs panels cause problems as things stand now, but if they could manage to handle multiple forms (which, I'll admit, I almost hoped for with Werewolves getting a "wolf" form) and expand the needs panel, it could be interesting.
Something that I used to do for a while (I stopped after my computer died from unrelated issues around Cottage Living) was force Spellcaster/Alien hybrids, because Aliens don't have different needs panels and Spellcasters don't have an alternate form. I used them to sub in as Faeries. And there were still some glitches (most notably, there were issues with making changes to both their human disguise and their alien forms. I was able to figure it out, but it required basically going into CAS twice, once from the Sim in question and once from a different sim in the Family and I don't remember which was which.)
I have to admit I don't think they'd do it, because I'm sure there are more things - even more occult things - they'd rather put their efforts into, but I certainly wouldn't say no.