This has been mentioned in various locations online and in a Youtube review I saw but to hone in this request and bring it directly to the developers, the basic argument is that this game has a lot going for it in terms of attention to detail and the ability to customize rocket designs. It also runs very smoothly but it feels like it's missing something extremely important, that being character. In other words, there's a sense amongst some of us that elements that would make the game more entertaining, are missing. I don't agree with that opinion entirely, I've enjoyed Juno/SR off and on since SR 1 and think that the game has a peaceful elegance to it that should be preserved but I think that it could be preserved while making some changes that add a bit of character or entertainment value without drastically altering the overall spirit of the game.
To at least try to keep this to one suggestion, that would be my suggestion, to give the game more character or a bit of spice but unfortunately that would be a vague suggestion if it weren't further explained or narrowed down to how this could be achieved.
I believe one or two more specific examples have been mentioned already.
For example, someone suggested death animations when an astronaut dies in the game. Another mentioned music that changes based on what's happening. If, for example, a rocket is over heating and about to explode, it may make sense not to have the same peaceful music playing. The music that does play in the game is great and seems very appropriate for interplanetary space but perhaps it could be faded in when exiting the atmosphere so that it seems a bit more special.
Not everything would have to be complicated. Simple changes like adding an alarm sound, perhaps similar to what was heard on the movie Apollo 13 when the Master Alarm was triggered due to the explosion that occurred, could go a long way to add a sense of urgency when there's a problem.
Changes could also be done incrementally, as they have been in the past. I fully understand how hard video game design is, I've dabbled in it many times myself as an amateur, but again, sometimes simple changes can go a long way to change the feel of a situation.
More complicated changes could involve something like a space race feature that has you competing with other space agency's to complete goals or risk losing funding. Or perhaps real time matches against AI opponents to be the first one to reach a planet or moon, etc. etc.
As it stands, Juno New Origins can feel a bit lonely or like a strictly solo experience. I enjoy it because I'm a space and rocket enthusiast which I assume many of us are, but things like this have the potential to open the game up more and offer more variety in a solar system that's already in place. In other words, it seems like the hard part is already done, it's just a question of... Can the appeal of the game be increased a bit by making changes that mix things up just a bit.
Lastly, I don't think it'd be fair to say that no effort has been made in this department, there is now a campaign mode and the developers here have clearly been willing to listen to customer feedback and make certain changes and additions to the game. What I'm mentioning is more about putting a cherry on top of what you've already done and bringing attention to you, a common concern I'm hearing about online, one which I agree with to some extent.