What I would really like is for someone to hack into Marklin's sounds and break their lock on their sound files. I have the Marklin 39241 which is a French EST locomotive that ran mostly between Paris and Basel. It has a station announcement but it is in German. I tell people that it simulates the time of the German WW II occupation but it is wearing thin. Would love to replace it with a French station announcement.
I believe other manufacturers are offering many more sound files and I think one of them has the flange sound but how would the engine know when it was appropriate to play it.
Finally someone must make a decoder with station announcements which you could play through a speaker in or under a station. A number of newer Marklin passenger car sets have decoders in them with station announcements. I have the Marklin 42790 which has a number of them and I created an Event which took advantage of them. Sadly in German. And the CS3 has station announcements and a speaker output so you could place an amplifier under the layout with a speaker and have station announcements any time. In fact you could use the real time feature of the CS3 to have scheduled announcements.

All sounds from inside, such as radio calls, can be quite unrealistic, but station calls are okay. I think M should configure certain sound functions so they can only be activated when stationary, for example station calls and leash, etc.

Personally, I often add extra sounds to newer Märklin locomotives. One of the first things I delete is the lokinfos file. Depending on what I want and need, I sometimes delete other vague sounds that are hard to actually hear what it is, eg like the sound for filling sand etc. this in order to make space for other sounds I want e.g. Locomotive cab talk, conductor talk, some station announcements, etc.
I also have a couple of sound clips with background sounds from passenger coaches, like creaks, vibrations etc. When I update the sound projects on steam locomotives, I also take the opportunity to adjust the steam chuff volume balance between normal running, loaded and unloaded, and idle. as these settings are only transferred to the mSD3 together with the sound project, and can not be edited by the CS3 etc.

For the 39490 and 39491, I found a video clip where they shovelled coal on one of these locomotives and I extracted that sound and replaced the standard Marklin coal shovelling sound. And of course made such that I can vary the length of the shovelling after how long a keep the function active.
Several locomotives and some wagons have some unique extra sounds/announcements etc so if I find something interesting, I extract the sounds and put them into the eigeneBibliothek folder in the mDecoderTol folder structure, and use them in other projects. It's also possible to combine several short Marklin clips into a longer sequence. And I also miss some more French announcements from Märklin.
I often run out of storage space, so I look forward to the new mSD3.5 decoders.

Why not use a standard sound decoder as a station sound decoder? On the mSD3 you could also use the decoder sensor inputs to trigger some announcements and lights etc, when a train is arriving and/or departing. And you can use the motor control as extra aux outputs.

The track sound (click-clack) is speed-dependent in more recent Märklin locomotives.

On Marklin mSD3 you can configure if sound can only be played while the locomotive is standing still or only while moving forward etc.

And for those interested, you also have some sound libraries e.g like the BOOM Library’s TRAINS sounds. (contains sound clips that were used in the movie SNOWPIERCER)
https://www.boomlibrary.com/sound-effects/trains/
But it's extremely costly for just a few sounds.

And if someone wants an eleric horn blast sequence from a traxxx engine, you can extract the sound from this clip:
https://www.instagram.com/onrailscandinavia/reel/DQ7dddnjuH9/
Sounds like the train driver enjoys his job.

Isn't that just a normal Fx Sound Decoder? ESU 58219? Zimo FS850? As rhfil shows, every station on every layout will need different announcements so a pre-programmed decoder is kind of worthless. Cheaper blank decoders and good programming software are the move.

Of course, the other option is to side-channel the sounds by embedding a BT speaker, or even something like a Raspberry Pi with mono amp shim.

I guess the peak would be to hook a Pi into DCC and have it listening for commands and railcom messages, then generating station announcements on the fly with TTS software based on what you tell your trains to do and where they are. You'd only have to give it a library of location names and stock DCC addresses for it to extrapolate from that.

As for me, I want more sound-fitted rolling stock. The new Hornby tavern car would be infinitely cooler if it made 'drunken revelment' sounds when stopped by a platform; and a metre long freight train will sound even weirder if only the loco makes Brake and flange noises. And, operating noises are the only thing I think the Start-Up cranes are missing. And lets all not kid ourselves - the Start-Up "Bat-signal" van would be way more fun if the Batman Beyond theme played when you triggered the light from your MS2.

I loved the concept of Hornby's TTS van they did a few years back - but the actual models had almost no redeeming features - ancient tooling, worthless couplings, and pickups so bad the van didn't roll any more; and the decoder and sounds themselves were laughable in quality. A "Start-Up" or "Railroad" grade system with modern couplings, a better sound decoder and speaker, and good rolling performance would be quite appealing, even if the tooling was still dated.