The new mechanics

play boost

We already have automatic enter the field effects (Lord Karthas, Infernal Vulture, Sentry of Light, etc); the Play Boost mechanic formalizes the idea of conditional enter the field effects. The development team headed in this direction with the change to Library Guards, and it seems it will be a core component of the Ancients Rising season.

non-shrine primary cards

I want to see where this goes. Non-shrine primaries are difficult to balance, and there are more coming in Ancients Rising. Even solid Primaries will be overpowered; imagine if you could make a deck with 20 Zombie Legionnaires or 20 Lizard Barbarians. Primaries need to be slightly weaker than other cards. If they're too weak, though, they won't see any play. It's tough to balance Spellweaver, and these will be the toughest cards to balance if we want them to see play without dominating the meta.

I imagine there won't be any limits on Primaries in Conquest - which means one Primary-based deck, if it were powerful enough, could be played three times with slightly different heroes and tech choices. Imagine, for instance, someone bringing two Spiders decks - one with the Valor cards and Trigon, and one with the Zombies support cards. Getting primaries right will be difficult, but if done right, it opens up interesting design space.