Custom UI Limitations
This is a test map showing the Custom UI limitation. If only we could get Blizzard to add the functionality to initiate targeted abilities from triggers, then Custom UI's would be much more feasible.
In the example I am using mouse move tracking to try and create a 3D splat (similar to what you normally get when casting a targeted ability from the command card). In single player testing it works okay, but online it's just not usable due to latency.
In one of my released maps I was previously using inventory items as part of the custom UI since you can click on an item to initiate a target ability, but it was too clunky as the inventory/item system is quite restrictive and not customisable enough.
The other limitation is that you can't hide units per player, however you might just be able to create an actor or model and do this and move it instead of a unit like I did in the example.
Awesome. One thing that would solve most problems would be if we could activated targetted abilities via dialog buttons. That would be all you need to change because it would then invoke the existing cursor/splat system that is already in the game for targetted abilities.
My game Battle for Sky Fortress has your standard hero abilities, but then also 15+ calldown abilities that always show on the HUD. It's the only way I can do it because of the command card, and 32 abilitiy limitations (not to mention that would be a much more time consuming way to do it than dialogs).
We'll be improving support for cursors in a future patch. Per player actor visibility is more complicated but we may add that feature it if needed by our designers. (Using flyer helper to accomplish it will cause visual desyncs or errors in replays).