It was something on my mind, I just need to mention a few things about your suggestion, I'm not an expert tho, these might be wrong.

• First user uploads a file onto the Steem blockchain which is scammed for viruses
  You can't upload a file to blockchain, blockchain works with json data, you can upload it to 3rd party hosting and get the link. (That will cost extra money for sure)

• Item Searching and Buying
  Searching is not an easy job if you want to do it on blockchain you can extract the data to database and make your queries there then it will be fine but for this you need to monitor every operation and parse the data and host this data aswell (parsing and hosting will cost you aswell)

• If a user wants to buy an item, simply click buy. If the user has enough funds, 98% of the funds are transferred to the user and 1% burnt and the user will unlock the ability to download the file via their account
  And where is the benefit for developer it would be fine to cut out some for the service you provide.

• This may be a problem as it's very easy to simply download a file and resell it for cheaper
  You can generate license files but you can't avoid warez.

• Grand vision
  It doesn't have to be my favourite artist, if you can provide a marketplace then it's just fine for me. If you can avoid steemit's greedy approach somehow. Then it will easier to market and can be expand to non-steemers, you can help steem growth this way.

And there were already a few project that you can host and sell things I just couldn't remember their names right now, I'll update when I remember.