Your assumption that the newer mechatronic units would have different inputs is flat out wrong.
When DQ250 a Cxx mechatronic unit goes bad it is always replaced by a Fxx unit, because Cxx are out of production for a long time. Has been like that for ten years or more.
Same for DL501 with Gen1 vs Gen2, if a Gen1 is bad it is replaced with a Gen2.

There is also a replacement software for every single Cxx unit ever made.

So if you wire it up as per the R32 and then flash the R32 software into it, then it will read the analog in.

Gateway sends 0x38A, not ECU or steering column unit.

Ok i was incorrect. I didin't bother to check FR, but it makes sense on older cars to ECU to send this because there is no steering column unit, nor BCM.
8P A3 (and G5) for example is different. Gateway relays this packet from convenience-CAN to drivetrain-CAN (among many other things).

I have never sniffed what mk4 gateway does, but mk5 works like this.
All CAN versions above 4.0 support this (CANVERS >= 0x9).
Drivertrain-CAN is indeed available on J527, but maybe it is only for steering angle sensor (id 0x0C2).
Are there any coding or adaptation options in J527 (or mk4 gateway) that you could experiment with?

Please forgive my ignorance - but if for example I buy a CXX from a MKV gti, and flash it with the R32 DSG software, the only thing that I would need to change then would be the gear ratio maps, as a bare minimum?

I confirm too what elRey said.
Ecu send 0x38A DLC: 4! I tried with CAN_R , CWKONFZ1 , CWGC, nothing change.
BUT BUT, good news today i tried with CAN_S and ....038a....not appear!
I search a lin to can convertor but no luck.
Only what i found is a lin to uart , but lin protocol is hard to find too.
We can not put the steering wheel ring and controler on our mk4 platform because must add a can gateway and all others arms witch works different like ours with other confort controller.
I thinked to send the same canbus message like dsg knobs send on + and - but if you look in cxx file , you will see paddles had some specific maps so the dsg waiti other messages from paddles(j527 , bla bla bla) than knob + and - messages! And i think this can be confirmed again because cars with dq250 have or not paddles and steering wheel ring must coded different.
The easy way is to send on canbus the message. For the moment i don;t have the steering wheel ring and controler , but i ordered to try to sniffer it.
elRey are you sure what dsg waiting is 0x38A for paddels?

Other model of GRA, but i think this is for me7.5 witch work with old cxx model, we must see if the new cxx model (not analogic input from paddles) from golf 5 , passat b6 had the same structure.
[START_MSG] GRA_Neu,906,4,20,1,S,XXX
[START_SIGNALS] GRA_Checksum,8,1,0,U,255,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Hauptschalt,1,2,0,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Abbrechen,1,2,1,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Down_kurz,1,2,2,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Up_kurz,1,2,3,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Down_lang,1,2,4,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Up_lang,1,2,5,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Fehler_Bed,1,2,6,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Kodierinfo,1,2,7,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Neu_Setzen,1,3,0,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Recall,1,3,1,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Sender,2,3,2,U,3,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Neu_Zaehler,4,3,4,U,15,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Tip_Down,1,4,0,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Tip_Up,1,4,1,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Zeitluecke,2,4,2,U,3,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Sta_Limiter,1,4,4,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Typ_Hauptschalt,1,4,5,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Sportschalter,1,4,6,B,1,0,1,0,1,,,XXX
[START_SIGNALS] GRA_Fehler_Tip,1,4,7,B,1,0,1,0,1,,,XXX
[END_MSG]

You can always add a CAN filter between that module and the bus. A device with 2x canbus that filters or alters messages as you see fit.
No idea if there is something ready to go like that, which you can buy, but any micro with 2x CAN will do.

Did some sniffing and now worked out that J519 is sending 0x38A onto the bus also, I just plugged the sniffer in and left it running whilst I killed modules one at a time until the message wasn’t present. I have tried recording the module, none of the predefined options VCDS shows you yielded any result. Then went trigger happy and just started unticking boxes in the long coding in the hope I’d mash my way to success but unfortunately not.

Looks like I may end up building some can-bridge/MITM module. Before that I wonder if I can just remove the module from the powertrain bus. Not entirely sure what other info it’s sending to the bus