Mnh... Since the title is controversial changes, it should be fine to share one of my own may or may not be a controversial change ideas about the Monk... Proper Greased Lightning, I think, will never come back, and we are stuck with the dull trait, but I did have my own idea, before 5.4 did that ugly trait update, about a "fix" for Greased Lightning's main issue, that it could not persist through moments when bosses can not be attacked...
First, the third action of a combo still grants a Greased Lightning stack, but stack duration will be increased up to a maximum of (insert what ever number can persist through moments when bosses can not be attacked) seconds, while the third action of a combo will neither grant the full Greased Lightning stack duration, nor refresh the duration to the full duration.
Instead, the first third action of a combo grants only 10 seconds to Greased Lightning stack duration, while the third action of a combo after the first, will extend the duration of Greased Lightning stacks by 10 seconds, up to what ever maximum duration would solve the problem.
I chose to design Greased Lightning in this manner, because I think that it would be "better" than if it were brain-dead level of almost not possible to NOT upkeep and maintain, as seen with the Warriors' Storm's Eye or the Dark Knight's DarkSide.
Also, keep in mind that even at a (super) slow 2.5 GCD, that would be 7.5 seconds to gain 10 seconds, so as long as the Monk keeps their combos in flow, it would be easy enough to build up to, and stay at, the new maximum duration, while building up to that new maximum would be "essential", for Greased Lightning stacks to not be lost when ever bosses can not be attacked.
Side-note I: In the case of 10 seconds every combo being "too generous" or "too easy", it could even be just 7 or 8 seconds, to make the stack maintenance, and to reach the maximum duration, a little more difficult.
Side-note II: I think that it would also be ideal, if the fourth Greased Lightning stack is not restricted to and locked behind any action, which was Fists of Wind back then, and only be level-locked, like the second and third Greased Lightning stacks, while the Monk unlocks the fourth Greased Lightning stack at a much lower level than waaaaay up at Lv76.
Since Greased Lightning II is unlocked at Lv20 and Greased Lightning III is unlocked at Lv40, how about the Monk unlocks Greased Lightning IV at Lv60?
Related idea: A bit of a dare idea, in the case that the new duration maximum would be some ridiculous max like a full minute or some long time. What if the Monk would also be able to "spend" seconds off of the Greased Lightning duration, as a second resource along with Chakra?
First(?) Addition: A idea(not my own idea), worth mention. If the duration of Greased Lightning runs out, just one stack of Greased Lightning is lost, rather than all stacks of Greased Lightning are lost. / My own thought on this: after the one Greased Lightning stack is lost, the duration of the Greased Lightning stack/s that remain/s, defaults to 10 seconds.