I've seen quite a few stealth aircraft on the site, and have even dabbled a bit in making my own stealth designs. Unfortunately it'll be hard to gauge just how stealthy these aircraft would've been, or to gain the benefits of designing an aircraft in this way. With that in mind i think creating at least a simplified stealth system along with an improved radar system would improve the game.

first off, from what i understand, there are a few different ways stealth can be implemented in the game:
-A few ways to determine how susceptible the aircraft is to radar would be how angled (as opposed to rounded) the aircraft is, whether one of its surfaces is currently facing a radar source or not, how large the aircraft is, how far away it is, and whether it has a radar absorbent coating or not.
- An arcraft that is angled, small, coated, distant, and facing away from radar will be harder to detect and require more time to lock onto with missiles.

On the flip side, adding radar parts and avionics to an aircraft should allow it to better track not only stealth aircraft but any aircraft in the sky, as well as add a radar tracker to the HUD. A wide radar pod can be added to track nearby targets in all directions, while a focused pod can be used to track long range targets in front of the craft. Maybe a multi-radar pod can also be added that can switch radar modes or use both simultaneously, at the cost of more weight.

Finally, in order to reinforce the stealth mechanic a fuselage that can hold weapons and other parts can be added, which can store weapons internally in exchange for not being able to hold fuel or buoyancy. The fuselage can also be opened and closed with one of the activation keys. Holding the weapons internally will serve a variety of purposes such as preventing the weapons from being reflected on radar or being damaged and detonated while the fuselage part is closed and intact. As a bonus, it'll look cool on strategic bombers as bomb bay doors.

Admittedly it seems like implementing any of these features would be tough but would also enhance the game and make it easier to build really detailed and good looking planes. Out of all of the suggestions, only the internal fuselage can be built manually, and even then its tedious or even outright difficult to make an internal weapons bay thats both functional and fashionable. At any rate it would make a good addition to the game.