Boss Rush modes like Rushdown and Court of Blades are a new type of content the game has desperately needed and it is criminal that (as far as we know) neither are permanent additions to the game.

Not much more to say in the post. Like the Exotic missions The Whisper and Zero Hour which took years for Bungie to recognize needed to return to the game, there isn't content in the game quite like these new boss rush modes. I hope that Bungie doesn't take nearly as long to figure that out and make a permanent Boss rush mode.

Tangentially this applies to the semi unique seasonal modes like The Coil/Nether and the Raid/Dungeon events with Pantheon and (assumedly) Rites of the Nine. I desperately hope post-Final Shape Bungie put more time into expandable lasting content schemas and not FOMO ephemeral content in their new Dual Expansion model.

Edit: Are either mode perfect? Absolutely not. But with updates/iteration, both could be superb. Especially Rushdown which excellently utilizes plenty of existing boss fights players rarely engage with - or can't because of the DCV, which is IMO the root of most of the game's largest issues despite being a tool to fix other issues.