I think if attendance at IOA flags, they'll punt something over to the Toon Lagoon Theater, but I don't expect attendance at IOA to flag.
My only really qualm about the timeline (and some people are probably gonna hate me for this), is that I don't think a VB expansion in and of itself would be big enough to warrant taking up an entire year. It's probably on the scale of importance as the Great Hall to be honest, especially if it's just like two additional slide towers. It's not like the expansions to Disney water parks (when those used to happen), were advertised as the resort's yearly additions.