That does nothing for blm. Repositioning is about the loss of casts, for example of a melee/ranged dps moves they can move during the gcd of an ability to lose nothing and at worst it delays a gcd by a second. For blms unless you preplan your triple/swift cast(and assuming it's not on cool down) you lose the time (up to 2ish seconds) by canceling a cast and the time it takes to find finish moving to start a new cast(blm doesn't have a gcd shorter than cast time). Astral/umbral is easy to upkeep with transpose juggling during phase changes.