*shoves Leo and Usagi into the Playboy Mansion during some big Playboy Bunny party*
*watches Usagi lose his mind while Leo stammers and blushes*

But anyway. Mostly I'm just bored of the April/Casey thing and ok with fiction going in other directions. Either way, these shows are always kid friendly so it's bound to kept very light.
Really, just a subtle flirtation between them that they never really pursue beyond that could be enough imo, and sweet and innocent enough to be enjoyable. (Too bad Donnie is already at a point that he'd immediately try to go past that.)
Or, she stays single. (Imagine that.) Or some new guy shows up.