Sorry Scrabbler, but why? Do you think its soo powerfull for a bard to use the buckler and take Shield feats as well to benefit from both? If you make it so that you can't use both SWF and shields together, you can just as well drop the option to use bucklers (and what then about orbs in the off hand, as they currently work pretty much the same "shield" wise?). A buckler still offers little in defence, as it does not get much in the way of PRR or MRR even after this change. If a Bard spends a lot of their feats on it, let them. They still have to use only light weapons to stay in swashbuckler stance as well as light armors or robes/outfits
The buckler + light weapon choice is Key/central to the idea of the swashbuckler, if Turbine takes it away a couple of months after introducing it, why introduce swash at all in the first place?