I think it would be great if a spell caster who concentrated on a spell could drop concentration any time during a round. Not just in their own turn. It opens up more tactical options for spells even at the low level available during EA. And it will become even more useful if more high level spells get implemented later. Besides real tactical advantages it would remove potential annoyances where the rest of the party just has to wait for the caster to get their turn to be able to do something. Think a levitated creature is the only one left and the meele can just stand around. Or a hazard, or later wall-spell, blocking their path. Concentration can already involuntarily drop outside the casters turn.
The way to drop concentration was not obvious to me and it took a while before I found it. Tutorial or UI change would likely make it more easily found. If someone else is looking for it, it is a circle with a swirl on the big character portrait in the lower left corner you should click to stop concentrating.