There is a clear difference between Shrines and Divine beasts that ARE open dungeons without rooms and hyrule castle. Now come on now.
That being said, i'm sure the temples in ToTK will be similar to what Hyrule Castle was but more dungeony. Without being a closed area necessarily, a Zelda dungeon does need some structure to it which Hyrule Castle doesn't. There is no real progression.
(preamble: just to avoid any confusion, what I am and have been talking about is all just about broad possibilities. In no way am I trying to say all dungeons should be either this or that or the other thing, the beautiful part about all of this is that we literally could have everything!)
Why does there need to be structure? The cool and uniquely interesting thing about HC was that there wasn't a structure with a clear progression! Go in one way, find some high end gear, leave again. Meet that NPC at the stable who wants the royal recipes, go back in from a different direction, go find Zelda's diary and another hidden room, leave. Come back even later, this time from below, stumble over the jail and find the Hylian Shield, leave, get sidetracked and run into the Shrine on the way out! Come back towards the end, different entrance point, you're set on the big guy, to end things finally but your eye is drawn to that one tower you never went to earlier, step inside, TRAP! LYNEL! You make it out, heart racing from the close quarters fight and you climb the tower to face purple pig cloud.
OR you just do it all in one. You go in that one time and you don't come out until you've crawled through every nook and cranny. It's the BotW experience wrapped into a dungeon space.
I see no point or benefit in discounting HC as "a dungeon" in BotW. We don't need to even define what "a Zelda dungeon" is in such a limiting way. Imo this only helps people who like making top 10 lists on youtube or somesuch. Embrace the fluid nature of the play space! We could have one of these dungeons, one 1998-style dungeon, a set of Shrine-like puzzle/challenge boxes, a survival island, a swamp shrouded in darkness and so on... All in the same game, no problem!