This title has received regular updates every month since Threshold has been able to work full-time on MGD. The Caverns is the last story location and has been released nearly a year ago in v21, but development efforts since then have been focused on existing content before advancing the story, including notable changes to the underlying systems such as the NPC system revisions, the introduction of the Day/Night system, and other changes to the Town area such as the introduction of the new Blessing system at the Church that was divided between v21.5 and v22, although there were other mini-builds between v21 and v21.5 as well as between v21.5 and v22. Then major build v23 was the balance update that introduced significant changes to the combat system and overall system balance including changes to the economy, of course mini-updates leading up to v23 contained some balance work and introduced new characters or further fleshed out existing characters such as v22.2 adding Beris while v21.1 added Minoni's art and conversations to Elena.
New builds are either major full number builds such as v21, v22, and so on that either introduce new locations or otherwise include major changes, "minor" builds which usually either introduce or expand on an existing character whether this means adding their art, new content, or both such as v23.1 that added Kotone's art as well as a small amount of new content to the Kitsune as well as art for the Caverns and the Lumiren (these minor builds can involve quite a large amount of work and be equal to a major build in terms of effort and time invested just that the overall changes and additions do not warrant a full number build for one reason or another), and the final type of new build is the lettered builds such as the current v23.3b which are typically dedicated to fixing bugs and typos but have featured new art on occasion when it could easily be slipped in. Every month has seen a new major or minor build at the very least as well as however many lettered builds it takes to address the notable issues and typos.
Advancing the plot has momentarily taken a backseat to correcting game balance and other issues as well as fleshing out existing content given that the Labyrinth is the final dungeon before the story moves on to the Capital, which will be a major undertaking, so these issues needed to be addressed and sooner rather than later considering putting off system changes would just mean that much more work in the future as the title grows. There is one more planned mini-update in the form of v23.4 that fill see Elly's quest for Venefica turned in and also included plans for some level of romantic content with Venefica, assuming plans have not been forced to change. After v23.4 and whatever number of bug fix builds are necessary, work will likely begin on v24 which is very likely going to be the Labyrinth given that Threshold has talked about moving things forward.
That said, the OP does note that the thread was last updated on 2020-09-07, and Threshold, the developer, has a post on this very same page discussing the release of v23.3b for bug fixing and such. Both show that this title is still under development and provide very definitive answers to this question.
I do hope that you find this enlightening,
PhoenixGorthalon.
No real clue on how the Labyrinth will be in terms of the story exploration beyond having Beris and her sisters as the Guardians who we'll be up against. Although Threshold has stated that there will be no Minotaurs in the Labyrinth, and unless this was deception on their part, does make it seem like the Guardian siblings will be the only foes we'll face during the story run.
Elf Village is certainly something to look forward to as is the Harpy Village, but no telling when those side quest locations will arrive, whether either one will happen between the Labyrinth and parts of the Capital being released, between releases of Capital content, or perhaps even after the Capital but before the Casino's Dungeon or after the Casino. Similarly with true Harem elements, that will likely be reserved for the Housing system once the player has their own place and can start inviting the MGs to live with them, but no telling when that will arrive later. There could be some interactions beforehand for certain intricately linked characters such as Kotone and Feng as we help them work through their issues, but those are not really the norm considering how scattered most of the love interests are. We know general content plans but do not really have anything like a firm roadmap outlining when a particular facet will arrive beyond what Threshold teases and the order of the main story locations like the Desert and then the Pyramid dungeon will follow the Casino and then finally the Demon Queen's Castle, after possibly traversing the Wasteland around said castle.
More romance content is another delightful element to look forward to, although that's also part of the vicious cycle of balancing the workload between working on existing content, advancing the story and introducing new places and people, and working on underlying game mechanics. At least we'll have plenty of content to enjoy for a fair amount of time to come.
While this is not much, I do hope that you find this informative,
Psajchol.
Just a minor clarification, but there are three sisters acting as Guardians along with Beris. Sister #1 sounds more Amazonian, possibly a MILFy Amazon, and apparently acts the most like one would expect a stereotypical Hellhound to act and may also have SHRIFT vibes, Beris is sister #2 and the runt of the litter, Sister #3 was nebulous in concept but her being something of a mage type was discussed, and sister #4 is an enigma who intentionally had no information revealed other than she too may have elements reminiscent of SHRIFT. Given the way evolution works in MGD, all four siblings may or may not be Hellhounds. They're all probably canids, but depending on whether they were born as Hellhounds or born as some type of dog-girl and all went through different evolutions is unknown. There have been jokes about what if all four are secret subs, but this is unlikely to be true and Beris may very well be the only submissive in the group.
Just wanted to clear that up and I hope that you find this information useful,
Konstantinus.
Next update is practically guaranteed to be Venefica content and Elly's side quest turn in based on what Threshold has stated about a week ago. The only question at this point really is whether or not it will be handled as a single update or split into multiple updates such as handling Elly's portions in one update and Venefica's content expansions in the next.
This is not much admittedly, but I do hope that you find it at least a little helpful,
Volta.