Dragon Priest will definitely continue to be good. Its staple minions are incredibly solid and powerful for their mana cost, and Priest has a very versatile kit that you can use to tech for whatever you are currently facing in the meta giving the deck many options in how to be built, while still remaining its original strength. It also has a really good matchup against many top tier decks such as Patron and currently Secret Paladin.

I do think Secret Paladin will fall in popularity in a month or two as people start to learn how to play around Paladin secrets. I took it for a spin last night, and I found that a lot of people misplay a lot. They will needlessly lose minions to Noble Sacrifice, or just kill a recruit when I have avenge up and my only other minion on the board is a Shielded Minibot, just to name some of the misplays I see. If someone haven't played Arena then its doubtful that they have any experience playing competitively against Paladin secrets, so this is a sort of learning curve stage for the ladder, which has the effect at making Paladin much better than it actually is. Additionally, nearly all versions can be very weak if you don't draw your MC, so having a deck of shitty secrets is a high risk/high reward scenario in many cases.

Consider what happened to Tempo Mage/Mech Mage as BRM/GvG went on- Mad Scientist and secrets seemed insane at first, but since we've played them so much everybody and their mother knows how to play around Mirror Entity and Counterspell now so the decks started to drop in metagame viability even though their lists remained the same. The same thing will happen Secret Paladin, because while it's still a good deck, I feel it wins more than it should just because people are unfamiliar with Paladin secrets (and the deck in general).