It'd be cool if Demonic Fury was used to summon additional demon pets for a set duration, and they all had different niches for different situations along with unique effects that incentivised some kind of summoning "rotation".

So say for example you have one demon that does the best sustained DPS on a single target, and you pump most of your demonic fury into summoning that one over and over as filler, but then you have another that does less efficient damage for the amount of fury is costs to summon, but delivers it in a huge burst for key moments. Then perhaps there's another demon that gives you a long-lasting buff that you want to maintain, one that heals and protects you, one that does great cleave/AoE damage, and so on.

It could be made especially interesting if situations where you had high fury allowed you to summon multiple different minions at once, and the better your gear got the more often you'd be able to make this happen. Basically just make demons functionally more like the spells you find in a traditional rotation, but thematically cool and unique to the Demonology spec.

And now that I think about it, having every spell be performed by your demons would be radical as well. It just occurred to me that most of your special moves in the game Bayonetta involve demons and their various appendages swooshing out of portals around you and punching your enemies in the face. Something like that would be amazing for demonology. Just make every spell some variant of a demon appearing (either for a split second or a little while longer) and performing the attack for you.