Wow, I was about to make a thread with the nearly-exact same suggestion, luckily I did a search before I actually posted it.

My written-but-not-yet-posted thread:

[Sugggestion Summary]
Please, make Cure III GTAoE with blue circle indicator during cast time, if no target is selected by WHM.
If a target is selected, behave as it currently does.

GTAoE = Ground Target AoE. Just like Shadow Flare or Freeze, you get a shiny circle, you point at a place and cast away.

*snip* (because this thread already covered most of the reasoning)

Thanks and bump!