Are we going to be adding more category's to seasonal? We are heading into season 5 soon...

I believe it is because there haven't been any new seasonal runs since then. Basically no one submitted any season 3 runs. We are heading into season 4 not 5 btw. Possibly more interest again now that there have been some significant changes. I think a lot of people were just burnt out.

How do I submit a run for season 4 since there's no category for it?

Season 4 is open for submission now

Keep in mind - rules are still being hammered out with the item changes. So please be patient with any review/approval.