As a web designer, I'm probably going to sound crazy but I think sticking to one simple layout with at most color changes and using your own banner is best. Here is why....a lot of times people don't test they layouts thoroughly and then they don't always work well with all browsers or mobile devices. As well, it's important to brand Indiecart, especially in the early days, you need something that says "this is an Indiecart shop". As this will be a jurored site, your branding becomes important because now they know they are getting quality over quantity.

I personally think at this time, less options, more consistent layouts from shop to shop, making it clear where people are. The uniqueness to the individual shops will rely more on their products, they can still continue to brand themselves vis their shop banner, their about page and product itself.

I honestly think in order to grow amd provide the traffic each shop is reliant on the success of Indiecart. Indiecart needs to be well branded and trafficked. I follow my stats closely, well did I've been very busy lately. I had at one point gotten my etsy shop to Page 2 on google search using the search Waldorf dolls. My traffic did not increase from google much at all. All my traffic and business comes from Etsy itself. Or my Facebook page. When people discover Indiecart they will come and search here. Or as Indiecart gets listed on google like with hyenacart, it will be listed as a search, thus it becomes important to brand Indiecart, creating consistent shops, creating a sense of safe shopping, quality handmade items.

Those are my thoughts.