SL4?

I don't/can't speak for the company. Based on the announcement, though, my best guess is that there won't be a Storyline 4. If they were planning SL4, it seems to me that they would've taken this opportunity to announce it.

I think Articulate 360 is the way to go, because it offers so much more than SL3. However I realize that the annual subscription price can be prohibitive to some.

Along with others, I keep hoping that the company will announce some sort of payment plan. For example, like insurance companies, they could offer a pay-in-full price, and offer a pay-monthly or pay-quarterly price that charges a bit more overall in exchange for the option of paying over time. But, again, that's up to them.