I can understand the desire for google to want devs to recompile their apps, but I don't see the need to dump old apps from the app store... who cares if an old app that works wastes 12k if it only needs a single 4k page?
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In any case, I assume that there is something similar affecting Android.
I would natively imagine the kernel could trap that and remap on the fly, at the tiny cost of murdering performance. Is that untrue, or is the perf so bad that it's not worth it?
In the worst case, ~every memory access causes the kernel to need to fix it, causing every memory access to be several orders of magnitude worse (e.g. a hot cache hit vs trapping into kernel, wiping caches, at the very least hundreds more accesses).
EDIT: I see you suggested remapping the page permissions. Maybe that helps! But maybe it adds the cost of the remapping onto the worst case, e.g. the first 4kb are instructions that write into the second 4kb.
A less safe option would be for permissions to be a union in that region, as code rarely depends on a permission being absent. That would be quite the security hole though.