I still don't really understand why they changed his pants from dark green to bright orange from Z Epilogue to GT. Personally I liked the dark green better.
But yeah, I really wish they'd release figures more often. I absolutely hate waiting years just for a single character. When was Normal Goku first revealed? 2010? That's just plain ridiculous to me.
At this rate we probably won't see Android 18 until late summer or fall. And God willing they decide to release 17 along with her; it just wouldn't make any sense to release him a year or 2 later. But according to their long release schedule, if we're lucky, we might get Nappa late 2015/early 2016, and Shenron in Summer 2017. But not before they release color variants/repaints of pre-existing characters, of course.
As for other possible Figuarts they could tease us until then? I wouldn't be surprised to see Raditz, Buu, Yamcha/Tien, or even Bills (that would make the most sense, given how recent and popular Battle of Gods is). Maybe even Adult Gohan or Broly (didn't they hint at Broly as a possibility already?) Not holding my breath for any movie or less-popular characters.. unless they're planning those for the Figuarts Zero line.