Warlocks barely get anything besides neat clothes. I think Blizzard is just doing this to either ...
That made me laugh. Warlocks for mop got ridiculously overhauled where their far superior casters-- and will continue to get good fixes (aslong as a certain GC plays them). Each spec is entirely different from one another and provide such unique play styles and experiences to them that makes the game vastly more entertaining than any other dps class. Its a wonderful job done by the class designers for warlocks. Wish others get the same in the future.
I think this is a large part of it. Rogues got legendaries to help bolster their numbers, now we're getting the fire people were asking for.
^ The rogue population was bolstered as much as it was because everyone and their mom made rogue alts and came out of the woodwork to get the legendary for either pvp, to just get a legendary, or get the account FoS etc. That # is not plain people playing rogues as mains. This will only hopefully cause an influx of people making warlock alts to get to see the content. Green fire won't make people roll locks as mains, our extreme high damage, playstyle, and talent system will.
This post does make sense to the fact that if it were a 'class' legendary such as the rogue legendary quest chain or whatever etc. It would be appropriate and well put to have a "special" event or quest to accompany the end reward-- Now the reward being just green fire seems rather a Big Build up
for such mediocre result. (Not complaining I like having special !@#$, fine by me. Makes the game interesting just awkward a big thing for just 'green fire' that you could of model changed yourself years ago) Especially when like the OP stated everyone gets these implements in glyph form currently, its no big deal for them but it is for us. (Shadow ravens, spirit of redemption as a valk, etc)
I would hope this is a precursor to every class having their own "quest story experience" like previous days in vanilla.