Why wait for that to happen? IMO your best bet is to search for the
best hardware specs within your budget that is easy to unlock and root,
and already known to be well-supported by Lineage, and then install
Lineage as soon as you get it home.

I made the mistake of NOT doing that (cyanogenmod rather than lineage)
with my previous tablet (a Nexus 7 2012 model) and ended up with enough
personal stuff on it that I was reluctant to unlock the bootloader and
install CM because it would have required a fair amount of time and
effort to backup and restore my data.

Good advice, I had the same issue with my Nexus 5 and Google ended support before I'd upgraded.

If anyone's interested I've opted for a Xiaomi Mi 5s plus for $344 through Shopmonk's eBay store. It shipped from Singapore today so should be here within the week.

In a previous post Andrew also suggested looking at the Xiaomi Mi A1, which is an Android One phone. If anyone is interested, these are available for around $272AUD, which is a pretty keen price for the specs.

https://www.geekbuying.com/item/Global-Version-Xiaomi-Mi-A1-5-5-Inch-4GB-64GB-Smartphone-Black-385504.html

Note, neither Xiaomi device has 4g band 28 (700MHz), which would be a problem for some carrier's networks.