Apple wasn't entirely clear, but I believe it's only future ARM-based Macs. Apple mentioned it as part the selling pitch for the transition since the apps could now run "natively." This was part of the discussion for emulation and what not which was only relevant on non-Intel Macs.
By default only ARM Macs will fully support iOS / iPadOS applications and developers will have to adjust their current applications to work on macOS Big Sur (Intel). This was clearly mentioned in the Platforms State of the Union.