This is not really true, you simply tweak the regeneration rate of the boss. If hes not being damaged at a certain rate his regen increases by a certain %.
If your DPS is above 6000 DPS the boss does not regen or regens very slow ( 500 hps/s )
If the combined DPS falls below 6000 DPS the boss regens 2k /s. This means the boss is still "doable" but will take longer and have more chances for screw ups for raid members standing in fire...etc.
If the DPS falls below 4000 DPS the regen increases to 4k/s which would basically become a stalemate. Even less would result in the boss out regenerating your damage output.
This type of mechanic is much more player friendly then a hard enrage that instakills everyone. This type of mechanic also allows for the raids combined dps to "slack off slightly".. sure the boss will maybe go from 40%---- 42% ------ 46% and people will scream "Pick up the DPS , hes regenerating!" The raid then has a chance to turn things around and step it up a notch and turn a loss into a kill. Bosses can still be a challenge.
You could argue its the same thing as an enrage timer but I dont think so. Sure a raid could stack 4 healers but they would never be able to overcome the regen of the boss to kill it. The raid never gets insta-jibbed by a DT enrage. Instead they decide to lose a couple healers and bring more dps. Let the playerbase decide.
Dude, all you're proposing is a soft enrage timer. What's the difference, if you dont dps enough you die. Sure, enrage timers might be "lazy encounter design" but it's a lot less lazy than wow until 9 months after it released.