The party will be inside but the viewing will be in the same place - BUT - They can take on more people because there won't be any tables in the viewing space anymore!
The Official Everything SW's at DHS thread has tons of reviews from when people experienced the party during rain nights (the same set up as when permanently inside 7/10-forward). The only difference people speculate is the reduced body space within the roped off section (same place as before) due to the lack of tables outside. I was hesitant at first, (due to the reduced eating/drinking time) but after reading many reviews of the new SW's fireworks and how key it is to be situated in a good spot; I fully think it'll still be worth it. And, got great tips on that thread about being able to bring to-go snacks/drinks outside when you're escorted to the viewing section