I was reading through the Instant 8.4 guide and noticed this...
Wi-Fi Uplink
Instant supports the use of Wi-Fi as uplink to provide internet backhaul for the Instant network. The Wi-Fi
uplink is supported on all the Instant AP models, except for the 802.11ac.
...
To connect an Instant AP to an Instant-based WLAN using Wi-Fi uplink, the controller must run Instant 6.2.1.0 or later for 11n platforms and Instant 8.5.0.0 for 11ac platforms.
Is Wi-Fi uplink planned to be reintroduced in 8.5? I can think of a few use cases, specifically where mesh doesn't fit well but Wi-Fi uplink could work.