So this was posted on the WDWMagic forums just now.
I should stress this is just a rumour for now, but as the guy (?) says, if true it should be announced in the next couple of weeks, before FP booking starts for the end of August.
I’m just going to post it as it was written.
Short Story: On August 29, Tower of Terror and Rock ‘n’ Rollercoaster will be added to Toy Story Mania, Slinky Dog Dash and Alien Swirling Saucers as Tier 1 Fastpass+ selections. Star Tours stays a Tier 2. Smuggler’s Run still set to open as a non-FP ride. I am unaware of any other changes to the tiers.
Source: I’m staying club level for SWGE’s opening, and I decided to do the paid FP selections. When you do that, you actually get to make 6 FP selections 90 days from your departure date, so I was able to do that on Saturday. You pick 3 to be the “paid” FP, which you cannot modify or cancel without calling/emailing Disney Signature Services; and you get to make 3 “regular” FP, which you can modify/cancel just like any other FP selection. When I checked my app, I noticed that my selections did not quite match what I had asked for. When I emailed with my question, I was told that on August 29, the MGM tiers were changing, and that the new Tier 1 will be TSM, SDD, A.S.S., ToT, and RnR.
I am not an insider, I am just relaying information I was told in an effort to help folks out who are starting to look at FP planning for late August. Assuming this is accurate, I would think it would be announced in the next couple of weeks, because people will be able to start making 60+14 selections for August 29 around June 16.*
This is the link to the thread he started, in case you want to follow along.