I think Slash is finally ready to truly collaborate and be a part of Axl's vision. His top priority is to tour, his true passion. That and money so it's kinda different from the good old days when he could freely make power plays like playing a few notes of Fall To Pieces ideas to Axl and then not letting him use it ("allegedly") and also quitting the band, expecting Axl to beg him to come back cause he probably thought Gn'R could not exist without him. I think I'll be surprised with what Slash can tolerate. I wonder if that will extend to Axl keeping some Robin/Bucket solos or Slash playing the notes they came up with but with his feel. Probably not though.
But it's easier now, after 20 years and Perla and it's clear to everyone that Axl is in charge with Slash n' Duff getting to be a part of it. I think they are thankful/careful enough to make it work. I'm guessing Slash can't fuck it up too bad in the studio cause it's a Guns album so maybe he'll actually attempt to come up with compelling ideas this time. He needs an event to truly work hard in the studio and play outside his cockfort zone.
Cool thing is Axl seems to be impressed with Slash's playing on the tour so I'm hoping for a Slash opener like you said like RNDTH or Suckertrain Blues and maybe even a couple more riff based Slash n' Duff tunes. Slash almost always starts his albums with a bang. I hope Axl will allow it.
I also think Axl is still very much interested in more epic stuff, is attached to the unreleased Chinese material and will still go with the Queen approach (more is more, many different styles) so maybe it could be a hybrid of old and new material, an album that rocks harder than Chinese did but retains it's scope and has more of the Guns sound, but is still hella pretentious.