I appreciate the classic view of Bards, and think something like 'bardic inspiration' is still valuable. However, the BEST "shout"/"vocal" mechanic I've every seen implemented in a game(and what I hope Bards take inspiration from) are Guild Wars 1 Paragons.
https://wiki.guildwars.com/wiki/List_of_paragon_skills
This can allow bards to be more than a "buff bot", but more of a 'commander' on the battlefield (this can be adjusted to fit the bard theme more, but you get the idea). GW1's paragon had an immense array of buffs, targeted attacks, defensive skills and a lot higher skill ceiling because their shouts were 'reactionary', as opposed to just mindlessly hitting the same 60sec buff. As well, the mechanic for maintaining certain buffs, or receiving passive benefits like healing, were based on if a shout was used within a certain time frame.
What are you all's thoughts?