[Consolidating all the threads that are exclusively on this topic: in this thread and: the rest threads on it are closed]
After countless of threads and forum posts and after the great help of many commenters in this very forum: I believe I have reached a solution that handles the actual details of how the Raiding+ lockouts will work and: everyone knows the devil is in the details.
a) First of all the Raiding+ Keystone will be a global weekly lockout similar to how hard core raiding works; but don't worry about its difficulty as a gametype in general; it would start from practically LFR-difficulty and be flexible up to a level so everyone will clear level 1.
b) It will have a global weekly timer of X hours; for example: you have 8 hours to complete the raid this week; if you do complete it within the 8 hours you will upgrade your Keystone by +1 levels and on the next kill the loot from a boss will be upgraded.
c) It will be REPEATABLE in the same week; that's what I believe will be the ..key of success here; if you are a semi-casual guild you may reach heroic early but the hard cores may reach mythic early but even they will run out of week-time eventually.
Bonus advantage: AMAZING STREAMING OPPORTUNITIES for extremely-fast-"LFR" runs first week; imagine the hilarity of seeing the most hard core guild in the world going after lootbags; but also: it will have an end soon since they'll key-upgrade.
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Other design ideas that will probably (or at least potentially) improve it further and are necessary in the general context of discussion for the design:
1) Per-boss keys on the journal and per-boss on-kill-loot; that means you would change raid leader and improve your key further and on better loot (per-boss on top); it would be extremely pug friendly.
2) Not counting out-of-combat time at all; this is an absolute necessity for raiding especially for casual and semi-hard core guilds; it's probably a required improvement for 5man+ too.
3) The timer can remain global per-raid even on the per-boss loot and level system; it's probably the smoother option also for Lore; a kill of a boss may add +X hours to the raid-keys.
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Other resources and older locked threads:
A) threads:
Older thread (less fleshed out: https://www.mmo-champion.com/threads/2644791
Even older thread (even less fleshed out): https://www.mmo-champion.com/threads/2644436
The War Within general suggestions (PvE+ is not exclusive there): https://www.mmo-champion.com/threads/2645931
B) Previous text of this thread:
Mythic+ is so superior in its design in terms of competition that raiding feels like something coming from 40 years in the past before the game genre was developed; people saying the timer of Mythic+ is bad is just utter nonsense; the timer is the final element that makes it perfect because not only it makes competition truly clean and quick but also it fixes the worst problem of MMMORPGs since their inception: potentially wasting the entire life of people with grinding.
Now there's an issue of course; first: if you do make Raiding into Raiding+ (i.e. gain all the mechanics of timing from Mythic+) then it will be harsher for people wanting to be too casual because it can potentially be never-ending; but the only true alternative to not make Raiding feel primitive against Mythic+ is to just delete Mythic+ from the game but that doesn't sound right so it appears that Raiding+ is a necessity.
C) The previous thread on this topic: https://www.mmo-champion.com/threads/2646036