Providing template variables is the direction that Australian GST example was headed, by showing the VAT component. Showing the total price including VAT is more complex.
My primary objective is ensuring that any changes reflect what is best for all Storez users
I cannot assume everyone wants VAT displayed and therefore cannot expect users to edit such info out of their templates, so it will be optional.
There is still the major problem of deciding which country a guest is from before they checkout, so it will have to assume the Company Information you provide in admin settings - a problem if you're selling internationally.
There is no need to provide any more tax options as Storez already lets you create however many taxes you want by country and/or state/province, so you can already use different VATs for different product types.
(thankfully I only have to deal with 2 levels - it's either taxed at 10% or it's not)
(Using L_(LANG_DEFINE) in templates is a superior approach to language, so I'll continue removing L_LANG_DEFINE from core code and templates wherever I find them)