The general principle I would like the raid game to follow is "One instance for farming, one instance for progression." The key here is setting up which instances guilds in the different strata go after.
1. There will be four variants of each raid: 10-Normal, 10-Heroic, 25-Normal, 25-Hard. These four variants are mutually exclusive and share a lockout.
I think that it would be best if you could only attempt an instance once per week. If you are saved to the 10-Normal version, you cannot go to 25-Normal version. In Wrath there's a bit too much repetition. You end killing the same bosses multiple times a week. It was worst in Trial of the Crusader, where you may have ended up killing the same 5 bosses 4 times every week. Familiarity breeds contempt, after all.
As well, there is a lot of blurring about who is involved in which strata. Many people at Elitist Jerks believe that 10-Hard is redundant, and only 25-Normal raiders actually use that setting. I am not sure that is true, but making things exclusive will provide clarity, and will allow each variant to be tuned to the specific needs and gear level of its audience.
2. All variants are launched simultaneously.
This allows hard mode guilds to jump directly into the race. They don't get to practice on easy modes first. As well, it makes the race more linear, as they have to defeat every hard mode in order.
3. Gear will use the following pattern:
Each step in the pattern corresponds to however many item levels is appropriate. I think about 6 would be best. So if Tier 1 10-Normal is ilvl 300, Tier 2 10-Normal would be ilvl 306, while Tier 1 25-Normal would be ilvl 312. This is important because it means that previous tier's Heroic mode provides slightly better gear than the current Normal mode. Remember that you cannot do both Normal and Heroic modes of the same instance in a single lockout period.
So if we go back to the "one instance for Farming, and one instance for Progression" idea, what would the patterns look like for each strata of guild as a new tier of raiding is released (Tier 2 for example)?
Royalty guilds have beaten the previous Heroic mode. So they would dive right in to Tier 2-Heroic, and farm Tier 1-Heroic.
Aristocracy guilds are working on Tier 1-Heroic modes. They will quickly finish Tier 2-Normal and use that for farming, and then finish off Tier 1-Heroic. After Tier 1-Heroic is finished, then they can start working on Tier 2-Heroic.
Gentry guilds will work on Tier 2-Normal, while farming Tier 1-Normal. If they beat Tier 2-Normal early, they can start to nibble on Tier 1-Heroic.
Bourgeoisie guilds will finish up Tier 1-Normal, and then progress into Tier 2-Normal.
The key here is that the current Normal tier does not obsolete the previous Heroic tier. That, combined with the fact that you can only attempt one variant at a time, will keep guilds balanced between the two tiers. They will farm an instance from one tier, and progress in an instance on the other tier. Which tier is designated progression changes as instances are complete.
Instances should be dropped more organically. Rather than repeating the same boss multiple times a week, a guild will work on different bosses. There is always a path for progression.
4. Gear will use the same name and stats across the tier. Each piece will have a green tag designating it as Valiant, Challenger, or Champion, reflecting which item level it has.
Essentially, this extends the Heroic loot method used in ICC and TotGC to the entire spectrum. [Uber-sword] drops from the same boss in all four variants. However, the [Uber-sword] (Champion) that drops from 25-Heroic has the highest item level.
What this does is eliminate the possibility that a Best-in-Slot item might drop from a 10-man due to a unique allocation of stats. An equal or better item will always drop in 25-mans. This eliminates any reason for 25-man players to want to do extra 10-mans. As well, it reduces the amount of loot and different items models necessary in the game.
5. Class Sets will be 5-pieces, and use the same tokens as ICC. One token for 3-4 classes, and a token can buy any armor slot piece. However, you will not use Badges to buy tokens.
This makes Class sets relatively easy to get, with a minimum of fuss. 10-Normal will drop Valiant Tokens, 10-Heroic and 25-Normal will drop Challenger Tokens, and 25-Heroic will drop Champion Tokens. Trade a token in for the set piece of the correct level.
It's not quite as easy as TotC, because I kind of like complaining that Conquerer's Marks never drop. Marks in TotC seemed too mechanical, with no real surprise element or something to look forward to when it came to set pieces. At the same time, having specific marks for specific armor slots seems excessive, especially when it comes to armor slots that drop off the last boss (Yogg and shoulders, for example).
I'll finish up with other thoughts, including badges, in another post. But I hope you can see the general structure of the raid progression that I am proposing. I think Wrath went a little bit too far in obsoleting the previous tier when a new instance came out. I want to balance between tiers a little bit better, and get a little more of a linear progression feel back into the game. Especially with Heroic modes, it sometimes feels like you are bouncing around too much.