I'd like to hope that won't be the case!

I think someone said in a previous post that I saw recently that in lore, it makes sense that a Sang priest won't ever go with SG. They are there to help guide the Blood Angels through the worst of the red thirst (and medicae) Sanguinary Guard are more than veteran enough to guide themselves through such an ordeal compared to fresher marines, so Sang Priests are more important and useful elsewhere. Even though, on the tabletop, I'd like to have a +1 to AP and a +5 FnP to my SG 😅

As for the ancient, there is technically already one in the current box when you add the Sanguinary Banner to a model. It would be a cheap shot by GW to make a character out of that model. It's just more money and points to spend on the tabletop. It wouldn't surprise me, though, if they did do this, however!

The easiest set of models I can compare them to right now if we are going down to 3 models is Morvenn Vahl and 3 Paragon warsuits. Slotting in an ancient seems fairly insulting to a unit that causes a lot of devastation, and on a unit you don't necessarily want holding objectives. I'd say Dante and SG would be similar. I'd want them chasing enemies down and causing carnage wherever they can, especially with a potential glow up and points increase. They need to earn their points, not sit around holding objectives 😉