I think there's quite a few things that need tweaking to bring Cav into balance with the rest of the game.
1) Ranged Chars should only be able to carry 1 quiver of arrows/bolts/darts/whatever. The ammo in those quivers should then be adjusted to always be the same. For instance, why can someone carry 24 arrows, but only 15 Bodkins which are the same size? Make then both 24 and make that the max (unloomed) arrows that anybody can carry. With scrounging it should be more than enough and will mean HAs stop being the end game annoyance that they currently are.
2) Since HAs now only get 24 arrows (unloomed) I think they would deserve an accuracy boost. However I would couple this with an accuracy nerf for people on stationary horses. This would encouraged HAs to actually try skillful shots whilst on the move instead of encouraging them to continually stop their horses just out of range, fire a few shots and then move away before you can get to them. This has to be one of the most annoying HA tactics ever.
3) Add horses weights to their stats. Then use this and the horse speeds to determine each horses max momentum and base maneuverability on this. Right now I don't think Horses are balanced against each other so it is no wonder some of them are overpowered in the game whilst the average horse is not. So long as whoever picks the weights uses a bit a common sense then it should work out quite well and force Cav to really pick between speed, armour and maneuverability.
4) Add disarms to the game. A Lancer going at full tilt, hitting someobody for a massive amount of damage should have a chance of being disarmed. Link the disarm chance to the damage done when thrusting only and it will make sure this doesn't happen in normal melees and it is only a feature to give Cav something to think about and stop them being able to dominate battlefields doing the same thing over and over again. This would also apply to people stabbing horses that are charging at them, which would nerf 2Handed thrusts vs Cav which are currently OP. Standing directly in the way of a charging horse and thrusting a 2 Handed sword into the horses head (and then into the rider) should not be an preferable anti Cav method. It can be there as a last resort that leads to you being disarmed but nothing more. Since Spear thrusts stop horses rather than damaging them, this will not nerf pikeman against Cav.
5) Nerf 1 handed spear thrust damage from staitionary horses (as suggested by Overdriven). I agree with this suggestion so thought i'd include it in my list 
6) Add deployable stakes to the game
Do all that right and I think Cav will end up balanced
EDIT: Completely off topic but this was triggered by what I just wrote so figured I'd post it here. With regards to looming it would be interesting if you could choose how to loom your weapons. For instance, with arrows it would be good if you had to choose either extra arrows or extra damage. With weapons you would choose either speed or damage (or accuracy for bows) and with armour you would choose extra armour or decreased weight. This would lead to a lot more variation in weapons and could be quite good
1. That would require some major adjusting. Plus, HA's can't scrounge. Being up on a horse means you have to stop directly over a weapon and look very sharply down to pick anything up. It would be easier for foot archers, in fact I see a lot of foot archers who do scrounge.
2. As much as I like the idea of an accuracy boost. Not at the detriment of more arrows. Accuracy isn't everything as HA. There is a lot of skill in being able to adjust your shots relating to your speed ect. It's why I can out shoot a lot of HA just by constantly shifting my attack direction/speed. It takes a lot of practice to know how to change your shots relating to those two factios. It's also why I often get out shot by HA who ride very slowly all the time (surreal for example) because I'm not used to shifting down to that slow a speed whilst they always ride that speed. But regardless, as an HA, unless you are the very best, you will miss a lot of arrows. 24 isn't enough unless you get killed in the first 2mins of a fight.
3. I'm not sure how you would determine the weights of light horses between each other. And heavy horses are already very slow compared to light horses to take into account the weight I think. It's an interesting idea though.
4. From a realism perspective disarms would make sense. But from a balance perspective I'm not sure that would. You would have to make a lot of adjustments to allow lancers to be able to use close melee weapons. A lot of lancers have pure pole arm wpf. I like that you try to balance it against 2h doing the same though.
5. We agree then
6. Not a fan of deployable stakes. I see them as being to abusable and potentially very buggy.
I strongly encourage chadz proposition of "no rearing by polearms", hp buff etc. it would give the game a completely new dynamic, cav can actually be used as formation breaker.
I also encourage to see all classes being balanced against each other concerning organized battles and not rambo-style everyone for him-self play styles.
that would mean: nerf class abilities that foster lone wolf tactics, buff the classes abilities that make them highly effective in teamwork
cav-wise that could be:
-nerfs: speed and maneuverability, also movement highly dependable on terrain
-buffs: hp, bump damage or time the bumped is on floor (maybe even make them be thrown aside a bit), no rearing when stabbed
this would make the horse a huge part of charges against infantry formations, but also make them very vulnarable if they go on hunting alone, as the cant dodge arrows or get away if slowed down fast enough.
From the speed nerf that we originally had though (before rebuff), this makes it very difficult for any cav that doesn't have a shield. Archers simply aim for you rather than the horse and at slower speeds they stand a greater chance of hitting. If you're in a formation/big group this would make it even easier. You then get the other problem of, why shouldn't you have fast light cav? Most HA need to be fast light cav for example.
No lance angle increase until client side WSE.
Thanks for clearing that up.
