There were hints of such in the last real big thing DC did with Doomsday Clock; plans of future events with a Green Behemoth and Thor, God of Thunder. It could still happen, it's just really unlikely.
Amalgam was mostly terrible, but it had some interesting bits of ideas among all the detritus. The best crossover had Captain America and Superman freaking out at each other about how the world is visibly incorrect while the rest of their respective teams tried to keep them apart and explain everything was fine and it's always been this way.
I liked how Spawn and Batman did their thing and for a little while, in his books Spawns' split face was due to "a vigilante dressed in black in another city getting cute" but eventually they changed their minds on that and then pretended it never happened. I've read most of the crossovers these companies did, and the Best Of The Rest were Captain Atom and the Wildstorm universe, Deathblow/Wolverine because the art is amazing, and Wildcats/Aliens because it led to the death of Stormwatch and creation of The Authority in that universe. They never retconned it, not that they had a lot of time to do so after DC bought WS.
Gen13 crossed over with Spiderman and Superman, Wildcats crossed over with Xmen and the JLA, Pitt and Hulk went at it in a book (I think, I'm kinda blurry on if that actually happened or if it was wishful thinking in a comics magazine), I wonder if The Mask ever crossed over with The Maxx?