It's probably to do with the runtime files? Spine runtime was implemented into VS source code & it's unlikely that Dragonbones or Spriter will work as they probably require completely different runtime frameworks for them to function properly.
Nice heads up for those of us who don't know about the application though, cheers.
Maybe Simon or David might consider adding support for other sprite part tools in a future build. Seems Spriter is quite popular & a lot less expensive for the pro version than Spine which is
damn expensive in my opinion.
* edit #1: just looked at the website & it looks pretty nice. Html5 animation export sounds useful, so maybe that could be utilized in someway as we are supposed to have html5 export support in the upcoming next version of VS.
* edit #2: oh & it has mesh warping capabilities, very nice! very nice indeed!