Yeah, Prime 4 is the one that has been generating expectation for years and assuming it's really good, which should be the case, it will easily surpass Dread and any other Metroid game I think.
Being a 3D game, in first person, and all of that... well, probably means a bigger budget, and for that and other reasons more people will look into a Prime game rather than a 2D game, unfortunately.
I think Dread making 2-4 million would be possible and fantastic news. While Nintendo probably has higher expectations for Prime 4, which they will probably market more. That's where I'm a bit worried about because while it is definitely going to be the best selling game in the whole franchise, I don't know if it will be able to achieve 7 million for example. 5 or 6, yeah, I could see that. But more than that.... I feel that the game would need to be really, really good, like, platform defining title, a strong word by mouth and made it more into the mainstream, kinda like what happened with Breath of the Wild.