The Buena Vista Palace has multiple restaurants, a spa, and 90,000 square feet of meeting space. Due to that, there's no chance it will be flagged as a Hampton. Without massive changes in the restaurant, it couldn't become a Hilton Garden Inn because that brand includes a full, cooked-to-order breakfast for all guests.
Although not listed on their website or the Hilton, a third-party site (Otel) notes: "The hotel will undergo renovation throughout the property between 09/01/2015 and approximately 08/01/2016. The hotel will continue to operate a full service during this time, although there may be some changes and closures to facilities."
I foresee one of two things happening. First, the existing Hilton Lake Buena Vista might be re-flagged as a non-Hilton hotel. That sort of thing happens occasionally. If I remember my Hotel Plaza history correctly, the Hilton is the only hotel that hasn't undergone a change in brand. In that scenario, the Buena Vista Palace would become a Hilton.
In the second scenario, the Hilton Lake Buena Vista remains and the Buena Vista Palace would become part of the Curio Collection by Hilton. Curio is a new brand started in 2014. That brand is for upscale hotels, which means the renovation would need to be completed prior to an official rebranding.
