Effective as of this post, you may publish your Addon, without necessary explicit permission on other places then industrial-craft.net.
However, you must still create/manage a regular and active thread in the Addon's section, providing enough information/details to be of use to users without the need to visit other sites.
F.e. A thread along the lines of "I've created XY. More infos here: [your personal website]" is not permitted, for the convenience of the Addon users.
On the other side, you're of course free to create a wiki or a website with more detailed informations to your mod, as long as the thread gives enough information so people can effectively download, install and play the Addon.
You're free to host your files on foreign webspace and link them in the IC-Forum threads, though.