Linux on 64-bit ARM is most commonly used with 4k pages and 3-level page tables. This results in a 39-bit address space rather than the full 64-bit address space.
It's possible to use 4-level page tables and then you get a 48-bit address space like you typically have on x86_64.
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Linux also supports using 16k and 64k pages as the smallest unit. You lose compatibility with normal 32-bit ARM code and other advantages of 4k pages.
For security purposes, 4k pages are best for the most granular memory protection and reduced overhead for sparse memory usage.
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The big question is how many legacy binary applications left for AARCH32? I really double there are many ....
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Android is now rapidly phasing out support for 32-bit only apps. It will be quite realistic to start using pure 64-bit Android within a couple years.
We'll likely be early adopters to get rid of a decent amount of attack surface and to have slimmer deltas for the OS updates.