We do understand that you need the feature you describe, but that alone is not sufficient to define it as “essential”, which is why we haven’t implemented it yet. We take note of all feature requests, and we evaluate each one based on complexity, benefits, impact on the existing feature set, and how many users requested it. This is the first request for such notification, which would affect all users who run the plugin (most of which don’t seem to need it), we can’t just “jump on it” and add it to the plugin.
Last, but not least, we must take into account that the EU VAT Assistant is a fully functional, yet free plugin, providing a set of features for which other plugins and services charge a fee. As such, we need to keep it as simple as possible, and focus on essential features for which the plugin was designed.
Our policy is to focus on essential features that work, rather than a large set of features that might be acting up, due to the increased complexity.
In relation to the support you received so far, I would like to point out that we updated the EU VAT Assistant within a couple of hours from the original request, to allow custom code to intercept the result of a validation and perform any action, such as showing a message to the customer. That was a courtesy from our side, to make customisation easier.
Finally, regarding the chance of breaking custom code, that’s highly unlikely. We’re aware that WooCommerce itself is quite infamous for introducing breaking changes at almost every new release, but all of our plugins have been fully backward compatible at every update. In other words we don’t break custom code at every release, and your custom code will run just fine with it.
If you need assistance to implement such customisation, you can contact us directly, and we will be more than happy review your specifications and propose a solution.
For completeness of information, your feature request is still in the list. We don’t have an estimated release date for it, but we will review the list regularly, and implement it in due time.