At the end, it's shown that anyone who has bested a yautja in combat has been captured, frozen, secured, and stored in stasis pods, so you see Dutch(Arnold), Harrigan(Glover), and Naru(Midthunder) all stored in their own cryostasis pods - so i assume one of two things: it's nothing more than a wink-wink, nod-nod easter egg OR they realized the only way to bring both of those legends back was for voice-only roles for an animated film like Killer of Killers and wanted to give a go testing it out first, just to have a sequel with all of them in the next one; HOPEFULLY like the Predators movie (that i was personally a huge fan of) - where they're all dropped on a planet together to survive as a team.
i know this second option is much more likely and possible because Arnold has done more VO work recently - see Mortal Kombat 1, Secret Level on Amazon, Predator: Hunting Grounds, etc. but i don't personally see them doing Arnold in live action for Predator anymore, nor do i see them using any of the above people in an AVP movie (with the exception of MAYBE Amber Midthunder if they're playing around with the wonkiness of time and space travel) - as i do personally think Dek is being saved to lead an AVP feature.