They didn't mention new Class Sets, but they did mention on stream that you'll still only be able to use the Class Mastery and Class Sets of your base Class.
PC/NA — Lone Werewolf, the EP Templar Khajiit Werewolf
Good question, would also like to know if Crux is going to work on other classes.
I'm pretty sure Crux will only be applicable to Arcanist abilities. Only Arcanist skills consume or generate Crux, and Arcanist passives give you special effects for having Crux.
So if you were a non-Arcanist, then grabbed Herald of the Tome, you could use skills like Runeblades to generate Crux, Fatecarver to consume Crux, and proc Fated Fortune doing so — but since you can only subclass into one skill line from any particular Class, that means you couldn't also have Soldier of Apocrypha's "Implacable Outcome" passive if you're already using Herald of the Tome. You'd have to be an Arcanist to have more than one Arcanist skill line.
PC/NA — Lone Werewolf, the EP Templar Khajiit Werewolf
I get that Class Mastery should stay with the 'base' class. That's not a problem. Also the IA drops should curate to the base class.
But if you're playing a character with the "Herald of the Tome" skill line even if they're not an Arcanist, then why are you barred from using the set that buffs the Herald of the Tome line, while an Arcanist who traded away the Herald line for Dawn's Wrath can still wear it? In what world does that make sense!?!
I'm also still salty about U41 specifically locking the Class set styles when they were unlocked (but unavailable) in U40. Are we seriously going to be in a world where the primary indicator of your class is your ability to wear a facemask?!?!?
There is no better reason than this to just remove all of the Archive locks on Class sets, both the styles and the sets themselves.