Thanks for your suggestions.
1. We agree that Sellacious categories are much better if placed in module instead of component, This is already being taken care of. Sellacious 1.4.7 might come with this feature. Currently, You can use just layout overrides in Joomla to stylize categories. You wouldn't loose any changes on update.
2. Regarding the category system, We have added this into Sellacious suggestion list.
Thanks for your efforts in improving Sellacious.