For buyers, this move will make browsing for collectible comics by era less effective because searches will be less streamlined and include everything in the Comics category. Sellers will also have a harder time tailoring their eBay stores to niche collectors because their era-listing store subcategories will no longer match existing search subcategories.
This move also represents a bit of disconnect on eBay's part between how the company believes comic collectors browse their site in search of comics and how comic collectors use era labels in managing their collections. Some collectors choose to specialize in obtaining certain eras of comic books. The whole of the Comics subcategory holds a vast sea of comic issues, and being able to narrow searches by era could be useful when looking for hidden gems published in their time frame of choice. Additionally, there are sometimes several volumes of certain comic titles published throughout multiple eras. As an example, Flash has several volumes worth of books as well as multiple issues in the same era with Flash in their titles. Not being able to manage these titles with era subcategories could lead to confusion.