My impression is similar to yours that this hotel joining IHG unde Vignette umbrella isn't all "done and dusted" as they have been lingering and delaying this for a while already pointing to potential contractual challenges/ differences.

AFAIK, the hotel is refurbished and pretty much done and already asking rather lofty rates for Budapest so not sure under how much pressure they are to come into the IHG fold.

IHG is more under pressure in my book when the IC (one day hopefully) goes into full refurb and one can only hope when it comes out of that it'll still be an IC. Nothing for sure these days.