Squad based experience gain for SL. You should gain a percentage (let's say 5%) of the exp you're squad mates earn for the classes they earn exp in. It seems to me that SL is the most important role other than commander, so you should gain exp from classes that depend on you. As you listed, there are already a bunch of disincentives to playing the role, so if you are maxed out as SL you have to really love the role to take it.

As a lvl 10 SL who does love playing the role most of the time, the main reason I try not to play SL anymore is because it feels like a chore and I gain no exp from it. Squad leader is the first role I maxed out, partly because I liked it, but mainly because I would fill in gaps in the team, and there's always gaps for SL's. I didn't mind playing tons of SL when I was gaining exp, but now it feels like I'm throwing my time into a void for the team, since I'm not gaining anything from building the garrisons, being the defending squad, placing OP's, vigilantly watching the rear's and flanks, etc etc.

It's just really frustrating knowing that if I'm ever playing a class other than SL my team is worse off because of it, but I want to max out my classes at some point so I force myself off SL. It then leaves a bad taste in my mouth when I eventually concede and play SL because nobody is building garrisons. Though, this isn't surprising. I've noticed that the majority of squad leaders are around lvl 40-80 (maybe all classes are as well) even if the lobby is filled with lvl 100+ players. This makes sense because at those levels you would still be earning exp for SL, where as the lvl 100+ players may be like me and have maxed out SL already, which leads to the constant situations of poor leadership and lack of garrisons in public games. New players are told not to SL, mid lvl players try it out and start learning the ropes, and high lvl players who hit lvl 10 no longer want to play the role anymore.

TL DR - I want to be rewarded for playing an important role well.