Throughout different expansions and tiers, there have been different ways of progressing.
The first way was the Vanilla and BC way. No heroic bosses, just different tiers where each tier got progressivly harder. You had to gear up in the previous tier to move on to the next tier. You were known as a good raider by the fact that you had defeated Naxx or Sunwell bosses.
Next there was the Ulduar style, where each boss had a hard mode, but you had to do something different to do it. It wasn't simply clicking a button (except for a certain boss where you literally pushed a red button). XT for instance you had to DPS down the heart. Yogg you let the watchers not help you out. Basically the heroic modes had a little story behind them. This is similar to the protectors fight in the current tier where you kill them in a different order and get better loot.
Finally there is the style where you simply set raid difficulty to heroic, and the boss fights change.
If I had it my way, I'd mix Ulduar style with the BC style. Bosses have a hard mode, where you have to do something to enable it, and each tier cannot be completed until you defeat the previous tier. While this is obviously never going to come to pass, it's my preference. I do think however, that with LFR, players would still get to see all content, and this would bring back "progression" into the mix. The current system is a little boring.
Ulduar didn't have hms for every boss btw, just saying. I definitely prefer a design where every boss has a hardmode, I don't see a reason not to since any other design will result in several bosses being way too easy/hard depending on who it's tuned for (even the few bosses without hardmodes in ulduar turned dull really quickly).
I would prefer to have something creative (ulduar style) to activate each hardmode, but quite frankly I doubt blizzards ability to come up with something different for each boss (especially that doesn't impact the gameplay negatively). If it can be done, great, otherwise I'm just fine with the current hc modes, not a big deal.
Actually, I prefer "Mists style," the combination of click-for-Heroic for all bosses, with the added bonus of a few special "Elite" fights like Protectors. Best of both worlds, in my opinion.
The worst thing about Ulduar style hardmodes was that anyone could "start" a lot of them and screw the group... that was a real pain in pugs.
And, honestly, was the "Ulduar style" of Hardmode activation really that special compared to "click for heroic?" Many of the activations were "talk to this guy" "don't talk to these guys" or "click on this thing." The others were just to do the encounter with exceptional speed or dps to activate the Hardmode, or to kill the enemies in a certain order.
I think heroic dificulity for raid is the best, you set it, you know what you sign for. Ulduar hard modes were quite cool, but not all bosses have one, so hc difficiluty fixed that issue (and you can still change this before every boss).
Vanilla /TBC style was good on paper, but you really need to give some help for avarage raider, or they will stuck for eternity at some mid tier loosing best players who go for better guilds.
I love what they try to achieve in MoP, we have tier progression, and you can't simply avoid a prevous tier and raid current one like it was in the past, but also game helps you gear up faster and you have some nerfs in old raids, so you won't felt left behind for long time, and start progress in current tier in no time.