I go with some points you stated, but I don't agree on some like:
-'Disable manual blocking on all lances'- every other weapon, even the smallest sword can manual block a lance from full speed, so that would be kind of unbalanced!
The reasoning behind this simple. First off, you cannot block with the couched mode only lances. Secondly, it make lancers have to choose a shield, adding more risk to a lance charge and add a different factor to the game play. Lastly, it would be realistic. Lances were unwieldy weapons; they were not a staff you can twirl around easily and block anything and everything.
-'Weaknesses of Poke-Lancing: Cannot be used by all lances'- sorry but that's simply bullshit, of course you can poke with every lance, even every spear!
as other people have stated, you are incorrect on this issue.
-'Remove the cool-down period for couch-lancing'- That would mean I just ride around and kill everybody with my great lance, so poking is useless
No. Thrusting a lance is still the much safer option of the two. As I mentioned earlier, the number of weapons that can safely stop a horseman couching a lance is
much greater than the number of weapons that can safely stop an extended poke-lance. The animation of couching a lance reduces the length of the weapon while the animation to poke someone with a lance extends the reach significantly. We are talking a difference of over 60 length here.
-'Lower the required speed for couch-lancing. Since damage is tied to speed, this would balance itself.'- you can even couch lance on a sumpter horse or plated charger, so it's fine
While you can on a plated charger, one thing I have noticed is that you have to be going at full speed, and a slight change in ground texture will often drop you out of couched mode. One place I noticed this particularly was the classic map "Field by the river." I was using a steppe horse for the experiment, going at full speed towards an infantry with no spear holding the bridge closer to the castle. The kill should have been a given due to the lack of cover and the infantryman's lack of weapon options. However, when the ground changed to the bridge texture, I was knocked out of couched lance mode. I immediately turned around and tried again several times only to discover that it was impossible with a steppe horse and a riding skill of 5 to perform the couch at this location due to the texture difference.
This is just one of a few examples where I noticed the speed requirement for a couch needed to be changed. As stated before, the lower speed would deal less damage as well, and would not be an instant-kill. Lancing at higher speeds would clearly be beneficial.