I'll reply to your comment in reverse points - if that's okay. Standard s3_tc/DXT Block compression can be done pretty well in real-time by the hw acceleration texture units on GPU in terms of mid-gen PS2-PS3 texturing, but to use it most effectively for quality texturing for PS3 onwards, each block of the original image is preferably used to measure signal-to-noise ratio against all (meaningful) permutations of chosen end-points (for the compressed block) in an exhaustive search to find the best fit. IIRC compressing with ATI's 3Dc half float compression isn't such a problem for real-time quality but I'm not sure if that's part of BCpack.
As for the first point, it isn't quite clear for UE5 type stuff, but my general comment would be, that I expect xbox to get a benefit with Bcpack on any traditional renderer (like this gen's games) where surfaces are directly lit and discontinuity noise won't be part of some intricate shader or compute calculation. My hunch about UE5 demo is that if it is async compute software rendering as tweets have said then BCpack hw acceleration wouldn't be usable without damaging the work scheduling of the async workload - as it would make compute dependent on the 3D pipeline, when the intention of async is to let tasks on compute, 3D pipeline and DMA transfers from disk intersplice harmoniously in the latency gaps of each of the other tasks to latency hide while sharing the hw resources.
Thinking about the async, we may find that the IO complex and SSD on the PS5 might be critical in just providing more time slice options to deliver data (at convenient opportunities) to keep the other two (compute/3D) working on time, as async compute is (AFAIK) is highly dependent on CPU schedule timing - as latency in the CPU propagates to the GPU async - so offloading IO from the CPU is a double win IMHO for async.