Jasmin, I fully understand your request, I have a friend who prints items for clients with their logo on it etc. She also wait for that feature.
About security possible issues, I have concern about anyone can upload a file that may harm your site, hackers are clever, they can cheat Joomla file type recognition. Not all people who visit your site/shops have good intentions. We have cyberwar in whole UE (UK included), you probably know that and why is that.
With URL field - you still be will be able to download file (pdf, zip, etc.), but it must be uloaded & shared by user first. I know extra step, but ...
As I know new field for product page are planned, maybe Ofi can ask our developer more details if he sits closer than me ;]