Currently we only provide focus traversal between UI elements that can be focused: text boxes. The lack of focus traversal comes from Spine using its own UI toolkit. It's actually a feature requiring fairly significant effort. Besides "doing the right thing" when tab/shift+tab is pressed, we also need to have a "focused" state for all UI elements. That means checkboxes, buttons, select boxes, and ALL other types of elements. Further, once elements can be focused, it would make sense for some elements to have keyboard controls, like up/down for a focused select box.
In the near term maybe we could improve at least some of the situations using hotkeys.alt+<key> is a common shortcut for accessing a function by name, usually application menus, at least on Windows and in a traditional application. Spine even supports alt+f to open the main menu, similar to opening the File menu in a Windows app. Anyway, in your example, alt+R could toggle the checkbox until we can find the time to implement focus traversal and keyboard control. I do think that is worth doing, as each switch to/from the mouse/keyboard makes using the application harder/slower.
