Years ago I suggested a talent that synergizes with getting your shield broken. Specifically to get people into the habit of using their shield at all. If you can encourage people to actively try to get their shields broken, they'll at least occasionally perfect guard or learn when to use it to block a destructive attack. There's a few different ways you can do it to make it worthwhile to get people using their shield and having it break, especially since a shieldbreak isn't something you'll be able to abuse constantly.
Shattered Strength - After your shield is broken...
... temporarily gain # defense?
... your next attack/skill gains % damage?
... restore # EP?
... your next # attacks are guaranteed crits?
Ideally you don't want people to get their shield broken, but it's a carrot on a stick to steer them towards it. You can give people all the "After a perfect guard..." talents you want, they're going to be ignored if no one is any good at perfect guarding to begin with from a lack of shield use. Anyone can get a shield broken, though.
I would like more things related to the shield that aren't just passives.
Right now we have things like shielding allows you to move faster, bigger perfect guard window and I think perfect guards restore EP, but I would like some actual skills that involved using the shield more (not necessarily strictly for defense).
Maybe a skill that's like the boar charges, where you rush forward (aimed with the target reticle like for meteor, weapon throw, blink, etc), and you dash forward towards that location, shoving enemies and bouncing projectiles out of the way with the shield as if they had been perfect guarded. Two handed users have a similar skill that can shove enemies away, so I don't think something like that would be too difficult to program, but for each enemy and projectile shoved/bounced, the shield takes damage (so you can't spam it willy-nilly). Instead of dealing damage based on your attack, it deals damage based on your defense and the "hardness" of your shield (shield HP, basically). Would go in the offensive utility tree.
Maybe another skill that works is a temporary buff (which I'd like to call Bulwark) where for the duration, characters when they shield, protect all sides of their character and their shield gains a resistance to damage taken. This would help a lot, especially in some areas like the desert where you are being attacked by literally all sides all the time. Something like this would definitely encourage using the shield more.
I know barrier exists (and I don't like its existence to be honest -- it is easily one of the best skills in the game that just works for literally every single character regardless of the situation or circumstances and only serves to make shields feel moot and only one character in a party needs to have it for everyone to benefit from it), but I'd still like to imagine a skill like this would be useful for a lot more aggressive builds that wish to avoid damage without completely retreating and could be useful for less mobile characters, like some two-handed builds that are slow and so may rely on those perfect guards for fast charges. Would go in the enhancing utility tree.
And a final utility skill I can think of off the top of my head is a skill where you throw the shield and it circles around you (3 times + 2 per skill level or something), with higher charges creating more shields that surround you. These shields deal a small amount of damage to enemies and block projectiles and attacks (if the attack hits the shield). Each "attack"" blocked breaks the shield that halted the attack like it was guard broken and it will disappear, but will also enable the caster's equipped shield special effect (if applicable) no matter what. Would go in the defensive utility tree.
Just throwing some ideas out there on a whim.