Great show as always... but about those issues of scenarios and reputation that you guys mentioned, i think the answer could be somewhat easy:
Reward for Scenarios; REPUTATION!!!
Gives ppl a reason to run them, and gives the same ppl something else to do than dailies!
The reward could be a token that you can turn in to _any_ faction-quartermaster to get rep. The rep you gain from these tokens wouldn't even need to be a better/faster way to earn your reputation than the dailies are, I think most people would just want to earn them in some other way...
So if the tokens "worth" in reputation is low enough, ppl would have to spend more time on them "farming" these tokens each and every day in order to be a faster way than from doing the dailies would be. Many who still only want to get the factions to revered or exalted could either do both (dailies and scenarios) in order to speed up their "reputation farming", or ppl who dont have the time or dont feel like runnig the same dailies over and over again but still would like to contribute some time to getting their reputations up, have atleast that one other way of earning it.
The problem with something like a token system would then be that hardcore players feel the 'need' to farm scenarios on and on, because there is no daily cap on them. It also cuts out the entire idea behind certain factions such as Cloud Serpent (AKA How to Train Your Dra... Serpent), Nat Pagle/Anglers, Tillers, etc. I can certainly see progress guilds requiring their players to have X tokens ready for a new patch so they get instant-Exalted without ever having done any relevant content for it.
A better idea imho would be to provide the Scenario cache with a shot at old pets/mounts, maybe some consumables as well, but a lower chance (or without the added gold) as the LFG bag.
There's another problem I see if they just removed lockouts and made it so you can only get loot the first kill each week is something we saw happen when LFR first came out: Gear funneling. Guilds would have the ability (the "option") to say run their alts through normal once, then run their alts along with 2 or 3 mains so that those mains get all the loot, then run again with 2 or 3 other mains etc, to remove the concept of sharing loot, everyone would just get all the loot that's appropriate for them that drops. A 25man guild doing this just rotating in 3 or 4 mains in per run would essentially be able to potentially get 8 or 9 weeks worth of loot in a single week.
We saw this when LFR first came out with DS, but it was mostly brushed off as not a big deal since A) it was only LFR, and B) it wasn't as bad as the people that were straight-up exploiting to get multiple chances at loot on the same toon. But if this also became possible for normal and heroic gear then this would be a big problem. The guilds with the most time and the most determination to do the raids 8 or 9 times per week would have a definite advantage. Especially considering that this would mean that during progression if you're stuck on a heroic boss, you could kill it on normal, get gear, and then go back to trying it on heroic again (even if you're not eligible for loot, you'd still be after the wowprogress credit).
And just as splitting 10 and 25 would make running both "mandatory", I think the ability to gimmick the locks would also become mandatory as well, and it would cause A LOT more burn-out than just running the raids a second time.
Honestly, there is no real way to balance the two. There is no way to make 25 man feel worthwhile if the the loot is the same. (Unless the lock outs are separate). And there's no way to make 10 man optional under a separate lockout.
Frankly, I think it's time to give up and pick ONE raid size. Make everything 20man, so that 10 man guilds can merge and 25 mans don't have to trim much fat.