I don't want to, to be completely honest. Spine is the only app that (now) needs it, and I like to keep my OS as clean as possible. The required download is 66Mb, which will expand to considerably more. This seems more than a little excessive just to run Spine.
So I'm left in a position where Spine no longer runs on my system. When I pledged on Kickstarter, the trial worked just fine (i.e. no X11 requirement). The previous versions worked just fine too. Hmmm...