Opinion: Shield bash should be a Keystone
Seems like it would be neat for a Keystone, just adjust the stats accordingly, it could give you a small gap closer like Ekko's e when it activates to make it more keystone-like. Replace bone plating with a tenacity rune or something. (Maybe just move legend: tenacity here and make something else in precision?)
Edit: Since a lot of people are saying it can't be used by everyone, maybe cut back on increasing the numbers and add a way to get shielding from this keystone. Possibly get a small shield(5% MHP?) when an active item is used?

.
E

uses rune.
oh baby a rune for me?