I think we will get Thunderstrike Liberators (the concept art was used for Realms of Ruin) as well as a number of other 2015 models refreshed into new Thunderstrike kits. Anything that doesn't get Thunderstrike armour will be retired to Legends. Extremis, Vanguard, and Sacrosanct will eventually get refreshed, but not at the edition launch. They may prune a few units like Castigators in the new book.
I'm not sure we would get a new Lord-Relictor since we already have a Thunderstrike Knight-Relictor and Ionus - the original Lord-Relictor - has a new model. It could go either way, but if I had to guess I would say they will just cut the Lord-Relictor model entirely. There's also speculation that they are dropping the Lord and Knight distinction in the next battletome, since Ionus did not have the LORD keyword initially.
Vandus might be killed off before 4th edition. There has been foreshadowing to his permanent death in the Dawnbringers books and short stories.
Here's my guesses for what is being refreshed and what is being cut
New Thunderstrike model:
Celestant Prime
Vandus Hammerhand?
Neave/Knight-Zephyros (already done)
Knight-Heraldor
Knight-Venator/Knight-Azyros
Lord-Celestant (with a special character option?)
Lord-Castellant (already one in Toll's Companions)
Prosecutors
Liberators (already kinda confirmed)
Judicators
Retributors/Decimators/Protectors
Removed with no replacement:
Gavriel Sureheart
Lord-Relictor?
Lord-Veritant
Knight Vexillor (rolled into Thunderstrike warscroll)
Knight-Questor
Maybe Gardus will be thunderstruck into a Lord-Commander during the next narrative campaign.
On top of the refreshed kits we will get some brand new ones for Ruination Chamber units, but I don't think it will be a huge Chamber. I expect 1-2 units and 1-2 heroes, at most.