I feel like the addition of some sort of ranged stun weapon for security, like a taser, would be fairly useful. As a long-time fan of the vanilla game and not BTE, I fairly regularly host vanilla BT and rarely host with BTE. As such, it kind of pains me to know that BTE has so much more weaponry and clothing/etcetera. I understand that the vanilla game has a while to go before that could be the main focus, adding extra features and such, however I think that more weaponry (both lethal and non-lethal) should be added, along with extra clothing. Both clothing that would serve a purpose, like to give a choice to security between a light vest and a heavy vest, with obvious differences in movement speed and armor properties, and also clothing that would be aesthetic, giving players choices on what they want to wear for their job. As for weaponry, I really think that a long range stun weapon (or atleast a moderately ranged stun weapon, besides the syringe gun) should be added for security or the captain.
As the owner of a heavily roleplay focused server, self defense is important to our members, but no departments are allowed to carry any weaponry besides command and security unless it is absolutely mission-critical that they do. They also are held by a law similar to the castle-doctrine, where they have a duty to retreat unless they are in their own department, defending themselves and their colleagues. This means our security has to be on top of everything, all the time, and getting in close to use the non-lethal alternatives to affect an arrest can sometimes be too risky for officer safety. Lethal alternatives are possible, but its preferred if we can avoid that. It'd really be great if there were a security-based weapon that would be used for mid-range non-lethal engagement of subjects. This interest isn't entirely based on my own need, either, I feel like this could be useful in a multitude of situations in multitudes of servers, INCLUDING the long-range engagement of a creature that has come aboard the ship. With a mere stun baton, its very difficult to successfully incapacitate creatures that board so you can kill them without risking harm. A mid-long range stun alternative could be a literal life-saver for this kind of deal.
Also, from my perspective of the owner of a roleplay focused server, individuality is fairly important. Most people want to wear hats/helmets, however under our rules they cannot as it violates the dress-code. This obviously has much less basis behind it, but I think it would be a very nice addition to the game.

Another addition I think would be very nice which would be cable tethers. I know they've been suggested before, even by myself, but it's been fairly proven to me that they really would be a great tool to have during EVA missions.
More creatures would be great, possibly some that would disrupt ships systems with noise. That sounded like an interesting concept to me.

I think that the vanilla game is fun as hell, and I hope that some of these changes possibly get implemented!