Simultaneous fight against Vergil 3/Nelo Angelo 3/Angelo Credo plz.
But that would never happen because that involves remaking old bosses from old games.
Oh and if Nelo Angelo was ever remade his speed would match that of Credo/Vergil 3. DMC1 in general was slower paced but Dante is in fact at near his peak skill wise and the demons are actually supposed to be stronger/faster than they were in DMC3 where he was less strong.
The one other thing I'd love to see in this hypothetical 'DMC5' (apart from playable Dante/Nero/Vergil/Trish/Lady, and maybe a nonlinear mission-select system that'd have you taking on different jobs at the Devil Never Cry shop in exchange for cash/orbs/blue orb fragments/weapons/character unlocks/you get the idea) would be some sort of classic/arena mode that'd let you fight every enemy and boss fight from DMC1/3/4. You'd get basically infinite replay value.
I am down with open world, non linear DMC too as long as the game play is tight and mostly takes place in tight environments. And like I said, remade bosses would be a shit ton of work logistically. At most they can do a 2/3 remade bosses like the best from each game but not every boss. Personally I would be fine if they just remade the god 5 bosses.
Also wouldn't mind an accessory system like Bayonetta's got, to be honest, as long as it's just about tweaking the mechanics and not making you do more damage or take less damage or whatever.
DMC1 sort of tried to start the accessory thing but never really fleshed it out (Bangle of Time). This would be a good path to go down into.
An ex system attached to an appropriate style. I don't want Dante to have a perma-ex system like Nero but something else. Maybe just timings on attacks builds a special meter or reloads DT. Or even a dark/light system with just timings where you can build multiple meters with different properties (swapping OTF). Almost like an RPG where based on your mana pools you can unload a whole different combination set. Imagine building full dark/light for an ultimate release. Or you fight holy enemies so you build your dark meter for damage boost. Maybe even something where holy will disarm and dark will poison. If you design the system properly, you have just made the enemies more dynamic with personality (which DMC has suffered in areas). You don't want to get too carried away breaking Dante's mold but it would be a great single player style.
Oh ok now I know. This is in fact one of my ideas for the newer styles.
The Style button basically acts like a new Rev button for the devil arm equipped. There is no "charge" stance, you HAVE to just time the moves. Each Devil arm gets it's own element that you can charge but if you swap you would have to start from that weapon's stock. You still have the charges stored if you swap so you can basically build up charges among weapons and then unleash them all at once if you feel at once or one by one as you need. There would be orbs that shine just like with Royal Guard indicating you have a charge stored up for the particular weapon (stocks change color depending on weapon equipped).
I also have an idea for a Weapon Master style, where you just map an entire weapon on the O button as a style. Sort of like Dark Slayer style in DMC4 but fleshed out with more options to choose which weapon you want there (INCLUDING firearms if you want to). Allows for players who like to play with more weapons at once to have the option to do so.