I doubt the developers will implement any more sets, or their respective mythical enchantments. They have only been slowing down on the pace of new content releases, besides the Underworld. Sentinel Set was just plugged into the game behind a paywall of gems, whoever was familiar with the game files knows that most of the work was already done; all the assets were there all along.
They didn't even bother to give Sentinel's hand a unique super slash like Monk's Katars, or even a mode like Ascension wherein a player that does not spend real money on the game can have a chance at collecting the set. They made it exclusive to underworld chests, basically like crates in other games. That's (for me) a big no-no; but who am I to give my opinion. It's safe to say though that 4995 gems (5 × Chest of Souls Keeper) for the whole set is too much.
All I'm saying is don't get your hopes up too high. Even if they get implemented, they may not be as cool as the Set of Monk once had the privilege of being. They would most likely be nothing more than new skins of familiar equipment, just attributed a mythical enchantment that does some known function slightly better than normal enchantments.
I know this sounds pessimistic. But I've stopped being excited about this game around 2017, when Underworld was still fresh. Don't get me wrong: I still play it, I'm just no longer interested in seeing the new things that are being added to it.
Apparently they are planning for an update this month, we can't be certain of anything, but let's hope for the best.
Also, yes, this game have got boring since quite a while with updates that are not interesting at all, I'm disappointed with the Sentinel Set, it's technique and the way to obtain it. We can't just tell them to do more, they spend more time and people to work on Shadow Fight 3, after all.
But wouldn't they have separate teams for each game? I assume, then, that some people working on Shadow Fight 2 migrated to working on the sequel, which sounds quite sad. If I were a developer of this game I would not abandon it so easily. But I guess they have the stats, not me. Perhaps a look at the player count would reveal to me that Shadow Fight 2 is simply a lost cause at this point in time, and that SF3 is more fruitful an investment.
Yet, I'd rather have one good update a year than 3 terrible ones a month. Even if it's just one weapon with a move I've never seen before.
What do you think?