It’s almost certain we’ll hear more about this at WWDC when MacOS 10.14 is announced. I think 32-bit apps might still work in 10.14, though.
From the Apple menu, choose About This Mac, then click the System
Report button. From the system report, scroll down to Software,
then select Applications. When you select an individual
application, you will see a field titled ”64-bit (Intel)”. “Yes”
indicates 64-bit; “No” indicates 32-bit.