How do I dynamically change an autocomplete route for a field depending on another field's value? On my node edit form, I have a select field (Field A) and another taxonomy reference field (Field B). Field B is currently using "views" as a reference method to filter for the options. 

When the select field has a value selected, I want the taxonomy reference field to show a different set of autocomplete options. 

I was wondering if there was a good way to dynamically update the "argument" for the views reference filter for the taxonomy reference field depending on what was selected in the select field?
If I understand your question correctly, you may want to include one term reference field for each taxonomy you want included on the form. You could then create a template for the page and use Javascript to control which fields are visible. So if the user chooses Option A  it gives them one set of choices for the Taxonomy and if they choose B it gives them another.. 

You may also have luck with https://www.drupal.org/project/conditional_fields