Unfortunately, we can't support every person's specific or custom implementations for CMB2. Github issues are reserved for confirmed bug reports and occasional feature requests. Please review the CONTRIBUTING.md for support suggestions. Please also review the additional resources listed at the bottom of that document, as the solution you're looking for may already be present.
The taxonomy fields are not intended to provide an arbitrary list of terms to pick from, but are intended to be a replacement for the default taxonomy metaboxes. I.e. they are meant to set the taxonomy terms on an object. Any other use of these types will be hacky and/or buggy. I suggest looking at building a custom field type for this: https://github.com/WebDevStudios/CMB2/wiki/Tips-&-Tricks#a-dropdown-for-taxonomy-terms-which-does-not-set-the-term-on-the-post
Thank you for