Conceptually, Aliens and Predators duking it out is a great idea.
The trouble is, the Alien race isn't technological, they're not really conscious or alert persay, they're like a viscious virus, which makes the only viable way for them to come into the lives of the Predator species is to be harvested for sport hunting, or the Predators come accross a derelict ship and become infected themselves.
With those limitations, it then becomes complicated how you can incorporate humans into the mix, but you have to have humans because you need dialogue and relateable/enjoyable humans to make the ride more interactive for the audience.
I think the AVP franchise hasn't lived up to it's full potential becaus focus has been put onto the title characters and the human factor hasn't been properly executed.
If FOX assigned a writing team that is strong at creating engaging characters and story, with no fanboy ties to ALIEN or Predator, and had them knock out a solid script, I bet you'd get an AVP film that's strong enough to stand with The first 2 films in each individual franchise.
A solid movie like this requires a balance of story-character-action-visuals, the first AVP films have spent too much effort on the action and visuals to the point where story and character seem like a 5 year old came up with them. This franchise can't survive on the WOW factor of creatures and special effects, it has too much appeal with fans of the older films and is too departed from them to win them over completely. I enjoy watching AVP and AVPR, but mainly for a mindless 90 minutes of sci-fi escapism, but the A1-2 and P1-2 both had characters you could be interested in and care about and root for, and I don't get that from the AVP franchise.