Hi,
Yes it could be done, but improving the forums is not a high priority for me compared to other things I have planned, so don't expect to see this soon.
There are lots of places a person can upload a file on the internet and just link to it and very few situations where there is a real need to upload files in a forum.
In mojoPortal, you could create a page with a Shared Files module and allow users to upload files based on page edit or module edit roles, then the user could link to the shared files page in the forum post.
Best,
Joe