Quite an interesting mechanic indeed, maybe it has a few quite OP combos, but all things considered it kinda looks quite fun and actually helpful.
The only question I have is how it behaves with "timed" shields and with bonewall, does the bonus just dissappear or does the new shield break?
for bossitron, as far as i understand, playing the same shield again won't grant any new stats, as the type is the same, also, think of AW, it doesn't let you play it unless you have a weapon, maybe this does the same except it does it with shields