Update on December, 2017
It seems the icon theme development has resumed under a new leader Sam Hewitt (the lead designer of Moka, Paper and some more beautiful icon sets)
Here is the github repo where new development is happening https://github.com/snwh/suru-icon-theme
Are they under development and heading to Unity 8 someday or they were abandoned?
It seems, Yes, Suru icon theme is still under development. These are under ubuntu-theme project name. You can view the project page from launchpad here https://launchpad.net/ubuntu-themes. There are several bug fixings in 2016 as I can see. The binary packages it produces include
suru-icon-theme. You can even install it with the command
sudo apt-get install suru-icon-theme
So, I believe they are not abandoned.
To answer, will they land in Unity 8? is very hard. Even Michael Hall (A Canonical worker) said in a blog post of May 2016, he don't know about them replying one of the reader's question (I guess, it was you who asked the question there). He said (quoting)
Question: A few years ago some of the Suru icons has been shown – including folder icons, filetype icon etc. They were beautiful. Will they ever land?
Answer: I don’t know, do you have any links to those icons?
You also said
For some reason Ubuntu Phone's file manager uses the Humanity icons, not those presented.
It could be probably the design haven't been yet implemented. Your posted images were just designs.