This was suggested on the discord in the Suggestions channel, but I'm also going to expand this to other things as well.
The main suggestion was for blowdowns for steamers. Blowdowns are a necessary function of steam boiler operation. As water is boiled, only the water molecules actually evaporate. The rest of the stuff suspended in the water then eventually collects at the lowest part of the boiler, nearly always the foundation of the firebox, which is called the mudring(it is also helpful to know that the firebox is surrounded on all sides and top by water between the actual heating surface and the exterior plates of the boiler). This suspended stuff collects in this mudring and blends together to make a sludge, which must be removed periodically for boiler health(and safety). As a mostly passive option, the railroad men created the blowdown. A valve(usually two,one on each side of the engine) is opened(whether by someone on the ground beside the engine or by the fireman, some engines are fitted with both methods) and the boiler, which is at pressure, blasts out water through this valve. The sudden new route for release of pressure creates a current which drags the sludge out of this valve and shoots it out of the boiler. This however does reduce the boiler pressure by a large amount(I don't know the true amount, but rough estimate, a loco at full operating pressure of 300 PSI could be as low as 200-250 psi depending on length of blowdown), meaning performance drops if the engine is in motion/underpower while the blowdown is underway.

So far, the most common way of blowing down that I've found is just straight up shooting it sideways from the mudring as shown in the youtube video linked here: https://youtu.be/sq6iG-Kd2FA

Another way is by piping the blowdown down closer to the tracks so any large chunks of mud don't utterly clonk someone across the face and injure them. Various applications of this exist as well.

As seen here on Pere Marquette 1225: https://youtu.be/vIsHW7oPTCA

PM 1225 has a sort of blowdown muffler, designed to lessen the force of the blowdown, while not actually hampering its effectiveness. SP 4449 and the rest of the Southern Pacific GS class also were equipped with Blowdown mufflers which is more of a shield on them and directly just blows the mud onto the ballast

As seen on that picture(hopefully it shows) of SP 4450, the blowdown muffler is visible right behind the drivers and right before the lever linkage in the trailing truck brake system, that little rectangle with a pipe(or pipes) coming out the top and disappearing into the loco.

Now, the best way to implement this feature would probably to add another type of steam emitter that can be triggered, something like EMITTER_STEAM_BLOWDOWN_#
This would allow the modelers to individually configure their blowdown valves to best suit the engines, like my own TMW J class has SP style mufflers already modeled on so I could make them work as intended.

Now, as I said at the beginning, this was originally a suggestion for blowdown valves only, but I am expanding this idea. Having various emitters for steam locomotives would be useful. Currently, we are a bit limited in making the various appliances come alive by using the Safety Valve emitters to make things like the TurboGenerators spew out steam(speaking of the safety valves, I've found the current ones to be a bit... meh. Here's NKP 765, at speed, with safeties blowing https://youtu.be/_asx4MAdeXo ). Having emitters tailored to things like the turbogenerators(which would turn on around half pressure and stay on until the engine is shut down(no fire in the firebox)) and air pumps as well as other emitters giving out various levels of steam(steamers leak, its a fact of life. There will be steam wafting around the entire engine if the thing is operating). Having various emitters like EMITTER_STEAM_GENERATOR or EMITTER_STEAM_PUMP or EMITTER_STEAM_INJECTOR(both the pump and injector emitters would ideally emit steam on intervals(mabye coded in or specified in json) and not all the time) would help enhance the immersion of steam locomotives as living, breathing beings instead of cold machines like diesel-electric engines.

Examples of other possible emitter types, prototypes in operation listed below:
Turbogenerators: https://youtu.be/aNQwU3cSSQk

Air Pumps: https://youtu.be/tjtywWxg_l8

More can be provided upon request.

Thank you for taking the time to read this
-Admiral