I've been using nopCommerce since the beginning...and I love to see how nopCommerce has been improving daily.
It's good that nopCommerce implemented multi vendor support, but there are couple things that need improvement.
The way specification and product attributes work now can be very painful sometime when we a large store. My current store has over 100 product attributes and every time I add a new product I have to look through a large number of them on dropdown. A lot of time, I choose the wrong attribute by mistake. Imagine if I have over 10 vendors selling different products in different industry, the number of attributes could go up to thousands...this can give vendors very hard time choosing the right attribute. Another difficult thing is we have to add a product attribute before adding a product, sometime we have to go back to add it.
I think it is best if we could make attributes work similar to Shopify. In Shopify, when a product is added, an attribute can be input with any name, no need to choose from attribute list. I think this is very powerful and flexible.
With categories and manufacturers, one large store could have up to couple hundreds of categories and manufacturers. When a vendor choose a category and subcategory, they have to choose from a very long list. If we can give a vendor permission to see categories in their industry only. This will help much less confusion and mistakes for vendor.