In reality, shields area defensive tool first, and an offensive one second. They allow, among other tactics, constant defense, even while attacking. Unfortunately the game shields lack almost all of the defensive advantages their real-life counterparts have, and turn their use upside-down: They bring a bit more offensive options your toolkit, while not really providing anything defensively, and due to the general effectiveness of dodging and that some attacks simply cannot be blocked, actually lose there. Using a shield kit also reduces your effectiveness against many enemies, and particularly your damage output.
So I’d like to see the shields’ defensive options enhanced - a lot. As is, it has three distinct defensive advantages: extra Stamina (in reality, mostly useful for pushing, which you admittedly need to do a lot with a shield), a wide push/block angle (moderately useful, but with a little skill you can control even the lower angles well enough to not be really needed), and the unique property of being able to block Gunner fire (useful if you end up too close to a shooting gunner - always a mistake - and against Deathrattler; the only place where I often prefer having a shield). Minor advantages in exchange for reduction in dodge effectiveness and offensive capability. The first two cannot really be helped unless blocking in general is made more effective (a bad idea, I think, as it would likely promote a more passive playstyle), so the last one is what can be adjusted.
This goes in the right direction, at least with the active part, but would still be too strong (and again, would encourage sitting behind one’s shield passively). Tie this to Parry timing (but not the Trait itself, obviously) and it keeps the skill component and doesn’t let people hide behind a shield. Let shields block the damage from Bosses’ defense-piercing attacks, or at least part of it. Let us protect our face from Troll Bile and prevent blinding. And maybe, as someone else suggested, let us use the the shield to defend while using or charging certain attacks. I think these would give us a few more useful options to make up for what we give up, and actually give some unique stuff for shields to use.
Oh, and btw:
This was mostly already sneaked in: Elites actually do have a limit to their heavy attacks’ Stamina draining component, so at least with BCR and enough Stamina they can be blocked completely, without breaking one’s defense.