The engineering team is 2x the size that it was at the time of the Oracle acquisition. 8.0 is the release where some of the investments are starting to pay off :)
This limitation had to be lifted for CTEs to be reused, which is in the same labs release as the JSON functions mentioned here.
I haven't checked yet if it is lifted for CTEs only, or all cases. But CTEs are a replacement for most (all?) uses of temporary tables that I can think of.
We're very happy with 5.7 right now and 8.0 looks great. Our app is quite old so invisible indexes will be awesome for finding what we can get rid of.
When will the JSON and CTEs make it into "proper" MySQL?