I'm going to be experimenting with Aventis Firestrike in my Freeguild list. He won't be the general, obviously, but because he's a similar points cost and brings more utility than a griffon general (and is also fluffy) I'm going to trial him. Wings of Fire is a really important spell as I run a unit of 6 demigryphs, and my standard list only has a battlemage on a balewind to cast it, but that's vulnerable. He won't be as killy as a griffon, but my army has tons of damage already, so I think his utility will make him a better choice. It's ironic that he can be more useful in a non-stormcast army since he gains the Hammerhal command ability and spells.
Alternatively, the principle is the same with the generic tauralon. Granted it'll still be the same model. That way he can have Twinstone and make the griffon entirely irrelevant.
On another note, I don't like Stormcast collectively, but when it is a single demigod leading an army of mortals they get a lot more interesting and thematic for me.
My list building methods are always to make the army cohesive and competent, but not necessarily competitive. I'm also a Freeguild player, so no other factions are involved.
The list: