Just a fun little thing I was thinking about recently. Shield skill points above the shield's difficulty should reduce its encumbrance by 20% per point or any other type of curve (exponential, log, etc).
That means that a 6 weight 3 difficulty shield with a 6 shield skill user will move as though the shield is only 2.4 weight, although the 6 weight will still factor in crushthrough and block stun. Lower tier shields typically have lower armor and less health, so they won't last as long as if they used a 5-6 difficulty shield, and bolts will probably go through them easily. I think this will help bring some love to the crappier shields that no one uses outside of those with low shield skill (or in strategus), and gives a better niche for low armor shielders who move slower with +6 shield weight and get killed in 1-3 hits.
Extreme builds such as 12/27 will be a bit faster, but they are pretty weak/gimmicky anyways, and this could add some more fun to the builds that decide to get 9 shield skill and sacrifice in many other areas. + it's only a difference of like 2-4 weight most of the time, not much unless you don't wear much armor anywhere else.
To supplement this, a shield wall bonus buff for moving shielders with a smaller radius than the normal shield wall will allow a group of shielders to move smoothly together.