There's just 1 problem with a list of predefined categories though; it's centralized.
As far as I understand, the DGS (digital goods store) also won't have categories. CFB does not like this idea of centralization. (even though it would help the user)
I don't think it'll be centralized if each client decides what pre-defined categories it shows? Btw, you should make these categories a) as general as possible and b) perhaps only for large markets. For example, cryptocurrencies should definitely be a category. Fiat, stocks... that's all I can think of at this hour

Perhaps even more general categories such as "Most Traded (All Time)", "Fastest Rising", "Alphabetical", "Newest Assets", etc.
I think of pre-defined categories just as a way for users/issuers to get started with the most popular assets types (to make the AE look good, of course). Using tags, that will give the issuer and users unlimited freedom to sort and categorize assets as they please.
You could also add an option for a user to to link their client to a service provider's API, and perhaps grab a specialized list from their servers. While a nice addition, IMHO it's not a replacement for the tag system.
Pandaisftw