Doubt it is coming in 10.15
Simply given that Apple's track record is to give folk fair amount notice on such things. iOS kicked 32 bit apps to the kerb a full 2.5 years after Apple started to enforce the '64 bit only' policy for new submissions (and only a couple of months difference for updates) to the App Store. And this was after they told the world in October 2014 that such a cull was actually happening. So, 3 years from announcement to enforcement.
And they gave notice of the same bit-purge for OSX (or is it now MacOS?) In their June 2017 WDC address, thus giving folks around 2.5 years warning (given that they subsequently informed the world that 10.14 would be the last version to support 32 bit applications).
I really can't see them changing tune and issuing another edict that'll severely curtail the apps folk run on their Macs barely 3 months before 10.15 could be announced.
10.16 - sure that's a lot more conceivable, but again possibly too soon.