Endgame Raid-like idea

Hello Exiles!

Today I came up with awesome idea to add something like a "raid" with multiple bosses to the game.
So, I feel like doing Endgame bosses has no point. I mean, yeah, they do give a little more valuable loot and guarantee T15 waystones but.. That's just it.
Oh and by the way, I am not talking about Citadel bosses BUT my idea has something to do with them.

Cidatel bosses drop fragments needed to fight the Arbiter. WHAT IF every boss had it's own, let's say, Soul Fragment? And then, the right combination of Soul Fragments in the Realmgate would open a portal to the raid.

For example: You killed Asinia, Draven and Lachlann and collected their Soul Fragments. You insert them into the Realmgate and enter the map.

Example map:


Then, you need to kill bunch of enemies, then Asinia and Draven to open a gate to fight Lachlann. I don't have any suggestions for a loot they drop. It could depend on bosses.

Anyway, all combinations for a raid map would need 3 different Soul Fragments. There is a lot ideas you could combine bosses. Like for example:
- ritualistic: Ignagduk, the Bog Witch, King of the Mists, Deathlord of Blackrib Pit & Ekbab Ancient Steed, or Rootdredge
- fire: Rudja, Candlemass, Ketzuli or Bog Witch too
- melee: Blackjaw, Mighty Silverfist, Crowbell or Rathbreaker
- etc..

Forgot to add earlier - all bosses need to be killed on T15+ map in order to drop Soul Fragment.

Also, these Raid bosses would be harder, of course.

This would make it more tempting to kill bosses in Endgame, imo.

What are your thoughts? :)
xoxo

@edit - some raid maps may feature fighting multiple bosses at once, rather than one after another.