Moving will be made to interrupt spellcasting at a point in time...

[Majidah]

If you can get all my party members stand in front of me like if they were under anesthesia, i will be a good girl and stand as still as wood...

Bards in TP parties managed...

[Saomai]

Bards in TP parties managed...

i also played brd in ffxi, and it was my main. the thing is, brd hardly needs to cast a song to the whole party, mage has their songs while melee has theirs, and again, because fights last a bit longer, i can even cast different buff songs to different melee jobs because they stand pretty much still during a fight... mages STAY STILL 'cos they need mp...

it works for ffxi, because it is designed that way.

i don't think it will work well for ffxiv because everybody will be running because nobody really has a CAMP anymore, and it will be frustrating as your party members constantly run away from you, because chances are, will server latency and all, it might take a second or two before the server knows that you are stationary...

anyway, i think it is left to be experienced and get used to, it's just that if the dev is just trying to give us a way to cancel casting, i think this is a pretty lame way to do so.