I have been informed (thanks) that the Fujifilm X-T3 will have the same button layout of the Fujifilm X-T2. Also the form factor will remain the same, with just some minor changes. Hence, once it will be announced, you won’t really notice any difference over the X-T2.
For me this is a good news, since the X-T design is loved by many just as it is now. Fujifilm did create the X-H line appositely to have more design freedom and craft a more DSLR-like camera. But the X-T should mantain it’s current form factor.