While it's probably going to be a while until we see a new operation, I've been doing some thinking on the subject anyway. Specifically, I've been wondering why I've felt somewhat dissatisfied with the latest crop of operations. The awkward difficulty curve has certainly played into it, but it's not the only reason.
One thing that came to mind was the over-abundance of random circle mechanics. Back in WoW, the raider's mantra was not to stand in the fire, and pretty much since launch, SWTOR's equivalent of this has been "don't stand in the circles". Usually said circles are red, but sometimes they come in purple, orange and yellow as well.
However, when I think back to the early days of the game, said circles weren't actually nearly as common then as they are now. Mainly they seemed to represent enlarged enemy target markers, for example if someone was targeting you with an orbital strike or you were being pelted by some sort of missile barrage. Eternity Vault - still my favourite operation in the game - is actually surprisingly short on circle mechanics with the exception of the first boss, who is a droid and the circles mostly work in the way I just described.
But other bosses don't have them, even where you might expect it. When Gharj goes into a frenzy for example, things get painful in melee but you don't know just how far you have to step back to avoid taking damage as there is no clear indicator. And a big part of why Soa's last phase has always been so hard to tank is that there was no easy way to see where the pylons are going to land. You always had to twist your camera around to look up while also trying to manoeuvre the boss in the right direction and not stand in the wrong place yourself.
Looking back, it feels like the red circles really took off with the release of Explosive Conflict, which is where they started to serve as clear range indicators for abilities that still also had other visual cues, such as the rocks bursting out of the ground on Zorn and Toth or Kephess' big jump. In hindsight this was probably the best of both worlds, giving the player a good idea of what was supposed to be happening from an immersive point of view as well as giving them the means to more easily understand and deal with the encounter's mechanics.
Starting with Shadow of Revan however, it seems to me that circles and other target markers have started to simply become shorthand for "insert a mechanic here". The most egregious example of this that comes to mind is the Underlurker in Temple of Sacrifice. Just how does spreading out in a perfect cross around him protect us from taking damage from his ground smash? Hiding behind the fallen rocks to avoid his rage storm makes sense, but this doesn't. The mechanic's only purpose seems to be to make people step in and out of a ground marker.
Or how about the Colossal Monolith on Ziost? The entire fight is about running in and out of circles, but what does any of it mean?! There is some on-screen text about the monolith exposing power sources and trying to draw energy from the rifts, but none of that really serves as an explanation for why people have to run into certain coloured circles and then into more circles of the same colour and somehow this interrupts the boss's channel. It all just feels incredibly "gamey".
It may be funny to criticise operations of all things for what boils down to a lack of immersion, but to me at least that's something that does matter. The boss doesn't need to have a deep back story or anything like that, but at the very least I should gain some sort of understanding of what moves he has that make him dangerous and why. "Circles appear on the ground and they are bad for you" just doesn't quite cut it.