At this point, we know that the attractions and shows on the Rivers of America (Tom Sawyers Island, Mark Twain, Columbia, Canoes, Rafts, and Fantasmic!), along with the Train are down for at least an year due to prep work for Star Wars Land. They do have the trains out to be looked at, but they are not in operation. Likewise, I believe the Columbia is in dock and you can look around, but it's not "sailing" at this point. Also closed is the Autopia, but rumors indicate it'll re-open in early April. The Jungle Cruise is also currently closed and no re-opening date has been announced yet. Otherwise, I don't know what else will be closed in late April, but DLR isn't known for posting their refurbishment information very far in advance. I would guess you'll get your first sense of what might be closed when they start posting the operating calendar about 45-days/6-weeks in advance.