This post is basically a reply to several recent posts on current state of the sim and to the developers. Sorry it's so long and repetitive and I do believe I've posted some of this content before but I do think it's still relative.

If it's at all possible to do with the current game engine, I believe, a vivarium and pauldarium dlc's could generate more revenue for the developers as well as a major draw for potential new customers to the original title.
True it would require going in a whole new direction and more time devoted to it, but given the success of other games such as Planet Zoo in introducing completely different species of animals as dlc they have been able to continue development over the past several years.

If anything you have been too generous to us, the major updates you have brought out as free updates have been huge in the number of new fish species but when you get down to it they are after all just more fish and does not generate any new income in your direction. Yes I know, some people think once they purchase a game everything should be free from that point on but that alone doesn't cover the costs. People have to eat and that's all there is to it.
Everybody has their favorite fish they want to see but that goal is pretty much an impossibility to reach so more unique species such as jellyfish, shrimp, skates, octopus, loaches, snails, seahorses, amphibians etc. would be a huge plus.

Reading through the posts I believe many are in need of new decorative items to place in their tanks, ruins, structures, even the more silly ones like yellow submarines and deep sea divers, mermaids etc.

The ability to have dry areas above the waterline with new plant and animal species to fit the environment. This is where the vivarium and pauldarim ideas come into play and in real life many aquarists are interested in other forms of the hobby as well but think it's to expensive to set up and requires way more work to maintain. This is the perfect platform to follow that route with no real consequences.

A person can build only so many aquariums before you get to a point where it begins to look like just another aquarium. The one saving grace for me has been the ability for custom backgrounds.
Being able to place mosses and other decorative items directly on the glass surface would enhance those custom backgrounds considerably, including where you are able to have air bubbles coming from in your background. For example I have one background with several broken pipes and valves, having it look like bubbles are coming from those pipes would be neat to see and bring that 2D background to life.
Being able to place different backgrounds on multiple glass surfaces, one, two or three sides. Speaking of which, more 3D backgrounds please.

Perhaps in the meantime opening the game up for player created content on the workshop other than just aquariums, but for decorative items as well. Player "mods" have been what has made some games continue to generate new players. Just more content from people wanting to share what they have created and no paychecks to cut.

Some of these ideas may be impossible to do, but surely some could be implemented.

There are other fish tank games out there, but of the ones i've played or seen this one runs the smoothest, has great graphics and seems to have the best creature animations in response to each other and their environment.
I hate to see it in a stalemate and maybe going another direction altogether might get it out of the funk it appears to have slumped into, seems we got an update about every three month or so. Of course I can't speak for the developers and where they are on the project, but even a small update gives people hope the sim isn't dead and going the direction of abandon ware.