Just an FYI here Nicolas,
All other eCommerce systems have a feature for this available to their users. Although these mods or add-on's are not traditionally free, they are not extremely expensive. Furthermore, they have been designed by developers from within the U.S.A. and that is why I had to unfortunatley switch to another eCommerce system as the time involved in the configuration of HikaShop for the taxes was extreme. I hated to leave it though because is such a well thought out system and works within my Joomla! site (unlike now where I have to link out to my store).
A side note about product options: this feature is standard with the more popular eCommerce solutions that are Open Source systems. The only additional add-on (for a fee) regarding options is when a user needs to configure dependent options. Maybe you can find a way to at least make simple options an integrated part of all versions of HikaShop.
Still, very good work and I keep checking to see how it is progressing so that maybe I can return to using it when all of the elements that I need come together.