JMO, but unless RBG passes (or retires, but I suspect she plans to serve until death) in the next 6 months, I believe the next vacancy will be Kennedy's. Lots of well-sourced (-looking) buzz recently that Kennedy wants to retire and wants to be sure that his replacement will be solid.
To THAT end, Trump has hugely satisfied Kennedy by picking former Kennedy (and White) clerk Neil Gorsuch for Scalia's seat.
There was some sort of casual "open microphone" banter between Trump and Kennedy that came out in the last couple of days from some affair and they seem very friendly. Something about how grateful Kennedy was to Trump's family for how well they are treating some family member of his in NYC and Trump telling him what a great kid he is, how everyone loves him. Sometimes relationships matter and Kennedy might feel comfortable letting Trump replace him, even if they don't see eye to eye on everything.