As far as 20th level capstones go, the Bard seemed to have gotten one of the worst ones (basically, if you don't have any uses of Bardic Inspiration when you roll for imitative, you get back 1 use). Honestly, unless your party is trying to blitzkrieg through a dungeon, you should have plenty of opportunities to take the short rests you need to recover all of your Bardic Inspiration dice in between combats. If I were to redesign the Bard's capstone, I'd focus on improving the reliability of your Inspiration dice rolls.
Superior Inspiration
At 20th level, whenever a creature rolls one of your Bardic Inspiration dice, you can treat the die roll as if it were equal to your proficiency bonus.
As far as 20th level capstones go, the Bard seemed to have gotten one of the worst ones (basically, if you don't have any uses of Bardic Inspiration when you roll for imitative, you get back 1 use). Honestly, unless your party is trying to blitzkrieg through a dungeon, you should have plenty of opportunities to take the short rests you need to recover all of your Bardic Inspiration dice in between combats. If I were to redesign the Bard's capstone, I'd focus on improving the reliability of your Inspiration dice rolls.