For Dante I'd love to get something like the new Katakros model from AoS (just less static as he'd be in the middle of the fight with his Jump Pack, Axe and Inferno Pistol obviously).
The rules they gave Katakros are great too. Basically at full health all his attendands fight and he only contributes a little. When he loses wounds one after another attendand falls away but he contributes more until he finally uses all of his attacks and also uses his shield.
I had similar thoughts when I contemplated on what would be great to have in the next Codex:BA.
One defining thing about Dante is that he is always accompanied by the Sanguinary Guard. On the table, when you drop him with a squad of SG and make a charge with one but fail with the other, it looks very silly. Like, the Chapter Master charges into combat, but his bodyguards stand behind and watch, or the other way around. I was thinking about a Strategem that let's one's retinue automaticaly charge along with the Character, but I like your suggestion too.
I also had thoughts about a big model of Dante + Sanguinor on one base. Like a single model. Them fighting in tandem. But that would imply that wherever Dante goes, Sanguinor appears, and thats a little bit to silly.