If you trim the fat down a bit you could have a good list going here, but Ill just adress your original point about GK's making MC's not vaiable anymore. Ive played a lot against the GK recently, and theres a good few BatReps from the likes of Jy2 around aswell. In all honestly MC's are still very effective. They just need to be synaptic MC's. Things like fex's and possibly regular trygons are pretty dead but Trygon Primes, Tyrants and tervigons still have a damn good chance to stand up to the Knights. I would recogmend trying a list that only has synaptic beastys or a lot of shadows before you discount them alltogether.
Anyway the list.
Your prime usually wants adrenal glands and rending claws. This is mostly so you have something capable of killing walkers, instant deathing T3 characters and generally being a bit faster than usual. However since your particularly worried about GK, I recogmend going with toxin sacs (re-rolls to wound mostly, plus theyre good for dreadnight killing) and the lash whip and bonesword.
Im not sure venomthropes are the best idea here. Its very easy to get cover anyway these days and they usually require a shooty build. Id have to say these should be switched for thropes, considering youve got a real lack of MC's here.
The tervigon will need toxin sacs, adrenal glands and catalyst. Youll also need more than 1, on his own he's going to take every anti tank weapon going.
Im pretty sure those hormaguants will need to go. Minimal MC's basically means tervigon spam if you want to be competitive and you need tervigons and guants.
1 brood of genestealers will be fine too.
The shrikes arent competative at all. Theyre paper thin and if an opponent gets a round of shooting, even with something like bolters, theyre dead. Theyre also queit small so you stand to lose the entire unit to a S8 large blast which is problematic. These will need to go.
Because there are so many changes that would have to be made, Im just gonna type a list out if thats okay.
Tyranid Prime - Lash whip and bonesword, rending claws, toxin sacs
Tyranid Prime - Lash whip and bonesword, rending claws, toxin sacs
3 Hive guard
3 Hive guard
3 zoanthropes in a spore
Tervigon, Catalyst, Toxin sacs, Adrenal glands
29 termaguants
Tervigon, Catalyst, Toxin sacs, Adrenal glands
29 termagaunts
9 Genestealers - toxin sacs, broodlord
3 Biovores
Primes go in the Termaguant broods, and everything moves on up. Just try to keep the tervigons safe or you might have problems. And do try a list with SoTW on your big beastys. It really hits GK's hard.