Not posting in the experimental squad section for the simple reason that as things are put forth now these squads would be exceptionally difficult if not impossible to put together. Still things I would love to see brought to the table in my lifetime. Things like a Xenos inquisitor with one inquisitorial army unit choice, a Kroot mercenary bonded and armed in the service of the Imperium, a captured Tau fire warrior mind scrubbed and indoctrinated and equipped for Imperial service, an Orc Weirdboy implanted with a Mechanicum mind control device used to study the phenomenon of the Wagggh and as an Imperial weapons system. The list is endless and I will give other full examples of fun to play around with squads later. Hope you like the small glimpse into my twisted imagination.
And speaking of Orcs : a Nob and a Squig herder with a group of special Sqigs obviously some discretion would be needed in most cases like taking IG prisoners and sending them to do battle with other IG but with a bit of story fluff and Munchausen by Proxy syndrome even this would be a fun twist on cannon fodder. To sum up Orc Nob with a big shoota (have to have some crowd control) a Squig Herder and a mixed bag of Orcy prisoners on a chain gang. Say a couple Eldar aspect warriors, an IG or two, an Inquisitorial Flaggelant, a collared Termigaunt on a loooong metal stick, a Chaos cultist or a few. With a cry of Squigs to the front and by using the Munchausen thing squigs yelling waaaaaagh as they are pushed into battle you have the makings of the ultimate wierdboyz.
You say you don't like mushrooms on your pizza but prefer chocolate covered grasshoppers and sugar ants well the above trick will also fit well with a genestealer cult unit. Bear in mind when the hive moves into an area (unless it's a full on hive invasion) they either prep the way with non transformed cultists or leave them behind in the wake of the passing fleets. MMMM now I have a taste for roast Tyrannid.
Of course if you have leanings towards an extended warp vacation the mix-and-match options are unlimited anything and everything have the potential of being corrupted. Good time to bring that one necrontyr model you have sitting on a shelf or in a box thinking 'hmm what do I do with this' . Pair that with a couple now renegade IG and a Hormagaunt or 3 turned warp spawned beasts.