UnifiedPush support has been announced for Element X, and NeoChat
The official announcement was mentioned in Matrix's blog post:
Next release 0.4.2 should also be published on F-Droid with push support using UnifiedPush.
In other news, thanks to Joshua, NeoChat now supports push notifications based on UnifiedPush.
Interestingly, the Element X issue regarding implementing UnifiedPush, has not been updated, and there is no related merge request that I can find. NeoChat appears to have their changes buried in merge requests.