Here's the thing.
Let's hypothetically say that Henson has the partnership and funding they would need to get this project off the ground and this thing actually happens (which it won't). How the heck is the aspect of a film that you can easily ignore and probably won't see (unless you're one of those rage watchers that need to see how ticked off they should be) "offensive?" I'm not talking about a "George Lucas ruined Star Wars with the prequels" level of retroactively casting a shadow of convolution on the original films. I'm talking about a harmless sequel that (again, hypothetically that it would happen) can just be easily ignored if it actually does suck.
Now I get it. The movie speaks to people. People born like decades after the original film flopped and almost fell into obscurity if not for a growing fanbase on home video. It's a cult film that has a bigger fanbase than the huge hit Avatar would ever have. I mean, that one was beloved and parodied for all of a year's time in which everyone stopped caring. Labyrinth parodies and references popped up in a lot of media lately to the point Gravity Falls almost had one but Disney didn't think kids would get it. It's a big enough cult classic that greenlighting the sequel to a film that didn't even gross 20 mil seems like a good idea. This old film has value in it. I really like it, but am a bigger Dark Crystal fan.
Personally, I don't think one is necessary. Sarah's character arc is pretty much finished in the length of the film. Sure you can have all the subpar faux-Japanese comic book adaptions and gushy fan fics all you want, the movie is over, the story is over. By that mindset, I could care less if there's another Labyrinth. It's either be some sort of Hook knockoff or a less good retread of the original with Sarah's kid and someone else as the Goblin King. I mean, what? Are they going to say they drained the Bog or Eternal Stench and put in a nice set of condos? What more could the story add that wouldn't be a predictable "You're friends are still here" fanwank? Even if you can fiond other stories and further adventures to tell, don't get ticked off that their big budget officially sanctioned fan fic doesn't sync up with yours.
But as an annoyed Henson fan, I'll give you the reality portion. Here's how this is going to go down. The project will get announced and sound like it has initial traction. Two years from then, we'll get a cryptic update and hear nothing more from them for a few years where they'll say "this is seriously happening, really!" and have some production art and a couple cast members lined up only for nothing to happen for a few more years when you may hear something about it going to a new distribution company...then 10 years after the initial announcement, the project will be all but abandoned. 2 Years after that, it will indefinitely be cancelled, but with news of 5 other simple projects that should get off the ground but don't. Happened to Fraggle Rock the movie, happened to Power of the Dark Crystal, happened to Happy Time Murders. Even if you are tearing your hair out at the thought of a sequel film somehow destroying everything you loved about the original film, you have zero to worry about.