BuddyPress.org

You can use an xprofile field, I see no harm in it.

Of course, there are other ways.

I believe, by default, all xprofile fields under “Base” are required.

If you don’t want it required, create a new xprofile group to house this new field.

To check the xprofile value of this new field, you’ll have to do a little manipulation in PHP with it. You could use substr() to check for file extensions.