After playing Rhine in ranked for a bit (60 games), I've found a few things that could make the division better.
First of all, I believe it is unpopular because it doesn't have a lot of interesting units so adding new units would make it more attractive (even tman only has 3 games with it and they were all forced by twitch viewers).
- add one 1 point slot (instead of 3 points) to the infantry tab.
For a reservist division, it doesn't have a lot of infantry slots. You're allowed to upvet your reservists but if you do you only end up with less than 40 line infantry and that's not enough for the spam you need, especially if you want to use MP units. - add the Mirage 5 F Cluster that's in 5e.
It is very hard to face T72 divisions because you only get 6 potent ATGMs. You can spam against NATO heavy tanks because they can't contest the AMX 13 SS11 and their range but PACT usually has enough ATGM on tanks or IFVs to keep them at bay. - add a big recon squad.
The recon tab is very poor. Having a high HP recon unit (reservist ?) to lead assault would really help. By making it unique (lots of SMGs ? GSR on big HP ? LRAC F1 ?) you make the division more interesting by offering a special unit for the deployment phase. - add a decent dedicated AT squad.
It's really awful to have to rely on the Jager CarlGustav only to see it struggle to deal with a lone BMP1. It'd be good to have a spammable "reservist groupe antichar" with 2 LRAC F1 to mix with regular res units. - add a second card of fliegerfaust OR allow vetting of the HTM16.
The division is very weak to helicopters. You're often forced to sacrifice your mirage 3 to take out ATGM helicopters and that's not sustainable. - add a second card of reservist FRF1.
Those are good and one of the unique units of the division but only one card is pretty steep. - allow reservist famas to come in res. vabs.
They're useless right now. - improve mirage 3 AT.
Free vet ? higher avail ? it's awful right now - buff F3.
Too few ammo.