So I was having a bit of a think about this and perhaps it might be possible (with a bit of rebalancing). It's a common gaming mechanic that stuff that automates tasks or makes them more convenient has some drawback over doing it by hand so to speak, either in terms of time taken or quality of result of whatever is produced. Take the docking computer in ED for example; the benefit is that you can dock hands off but the price you pay is the time taken to do it - it is quicker if you do a manual landing.
So looking at the ADS in the same vein, I thought perhaps the ADS could come back with a few tweaks. Instead of the instant reveal of the honk it is something that you switch on and it does a progressive scan of the system. It starts to populate the system map with bodies in the order of proximity to the ship. The more bodies there are the longer it takes to fully scan a system. In terms of balance with the FSS the ADS:
1. The time taken to fully scan a system scales according to the number of bodies in it.
2. The time taken to scan a body in the ADS would be less than it takes in the FSS in line with the reduced information the ADS scan reveals (as before) compared to the FSS scan.
4. ADS scan would not give the discovered by tag (as before). To get the discovered tag it would need a FSS scan or a fly by close enough for auto resolution.
5. What happened to 3?
6. Perhaps the throttle needs to be zero while ADS scanning, or perhaps not. Personally I'm ambivalent about this.
3. Here I am. Sorry I am late.
Now all of this doesn't take into account the effort to implement it and support it but in principle how does this sound?
The thing is, the ADS 'honk' doesn't (and isn't being suggested to) scan a system. It simply reveals bodies present (as unexplored) in a picture.
The FSS 'honk' does scan stars (and other bodies in close proximity), but otherwise just does the same as the ADS except it reveals those bodies as energy readings on a spectrum.
The suggestion that only the ADS provided an instant reveal isn't correct, the FSS provides the same information just in a different format. Arguably, the FSS reveal is far more accurate and powerful.
The reason people are asking for the ADS to be brought back is simply to enable quite niche forms of exploration such as spotting stellar forge anomalies without having to scan everything first or to enable players to target bodies and fly to them if they don't find the FSS gameplay engaging.
For most exploration styles the FSS will be the way to go. It's easier and quicker to identify specific body types with certainty and it makes cherry picking those bodies easier. In short, it makes 'traditional' exploration quicker and easier, styles of exploration that FD likely knew from their metrics that most players engaged in.
Simply bringing back an optional ADS module that worked exactly as it did would not affect anyone who likes the FSS, but would enable niche exploration styles to be accommodated, at the 'cost' of having to use a module slot.