A little late to the party, social apps chain Frequency has enabled Async Backing and will now benefit from 6 second block times.
With a latency tweak, Parity Developer Bastian Köcher has been observed building parablocks in less than 500ms, resulting in 12 parablocks per PoV (Proof of Validity).
Ajuna Network has enabled Asynchronous Backing for both Ajuna and Bajun, game on!