This seems virtually useless in raids (current ones at least, and I suspect future ones). Remember it's not just about finding a place where you can hold still... that window of standing still has to be long enough to make it worth the cast time of the song. You'll be losing GCDs, so you'll need enough time to stand there in order to make it worthwhile.

T10 you might be able to use it during the add phases. Nowhere else really.Too much movement is required for tethers and charges.
T11 you move constantly. Can't think of any point it would be worth using.
T12 you could use it if the team doesn't have you handling redfires, fountains, etc, but most teams do ask that of bard precisely because they can move and attack.
T13 you move almost constantly. Flatten/akh morn doesn't require movement, but they are so fast by the time you got the song off megaflare/earthshaker would be up. Maybe you could use during parts of the add phase.

People are going to say "BLMs manage!" but BLM doesn't have to cast a spell just to get into "dps mode", which will then drop every time they move, forcing them to recast it. Realistically a bard will be casting this dozens of times in a raid, and I can't imagine it will increase their damage enough to be worth it.

This is talking raids of course. Dungeons and such? I'm sure you can post up and nuke away, but honestly who cares? Dungeons are rofl-easy and your dps really doesn't matter.