I don't really mind for Predators and Engineers having met before, but if they did I wouldn't be shocked.
Anyhow, I do like the idea of Predators having various home worlds in regards to their clans. In the way that Earth has many countries, I could see a Yautja solar system and each planet/moons serving different clans or purposes.
I feel like the 'established' clans have their own worlds and multiple hunting planets or training planets.
The Yautja in between those worlds with no establishment might be the 'space pirates' as I heard someone use the term on the forums before.
Yautja that just hunt to collect and better themselves, traveling the universe and living lawlessly.
Their origin shall remain just as much a mystery as the origin of humanity is.