You can embed cmdx in a library and distribute it alongside your tool. This has the benefit of not depending on anything external and guarantee the functionality and behavior of your tool. As well as enabling you to make changes to the embedded version of cmdx specific to your tool.

But, the user currently can't have two or more versions of cmdx loaded at the same time if their versions differ. E.g. one version embedded in toolA and another version embedded in toolB and maybe a third version installed globally. That's because the undo/redo mechanism is built as a Maya plug-in, and there can only ever be one plug-in by the name of cmdx. That's a bummer! And a bug.