That'd be crappy it'd pretty much negate up it's usefulness with the defense reduction
But that choice buckler idea Is interesting... I don't know if offensive natured pokemon would appreciate it though and I don't know any defensive mons that want to be locking into a single move.lol
Whimsicott and Toxicroak are examples that wouldn't necessarily mind less defenses for greater healing to mitigate Substitute dmg.
Also, he said Choice Buckler would disallow attacking moves. Basically, a reverse taunt that makes you total taunt bait, but with boosted defenses.
I think both items would be niche, but cool additions. GF needs to step it up bc most of their "niche" item introductions are simply "outclassed" rather than niche alternatives.