Hi Oscar
I think this could be a very good idea. Not only does the new URL structure look more SEO friendly for bots and also more friendly for users, creating a category page can be a great way at ranking an ecommerce site.
One of the main problems with an ecommerce site is the requirement for each product page to have its own unique content on it of some substantial length, let's say 200+ words. If you have hundreds or thousands of products, this quickly becomes a problem.
Conversely, creating a category page that covers your main search terms - eg "sunglasses", "sunglasses for sale" - can also cover some long-tail keywords as well: "best sunglasses for summer", "sport sunglasses" and so on.
In order to do that you should make your category page as rich as possible - include a healthy amount of content and even things like reviews and videos of some of your top selling products. Make it informational as well as promoting your shop, so that it could also be seen as an educational resource as well as your shop front.
I think having a static category page over a search result page to promote in organic search is a very good idea. Make sure it is content rich and worthy of ranking and that any necessary redirects are taken care of.