Are there stilll plans in releasing nand2tetris part 3, as Shimon says in unit 7.3 More Fun to Go ?
I don't see where any plans to do that were stated. What is the "unit 7.3" you are talking about? In the text, Section 7.3 is the implementation of the first part of the VM translator. The "More Fun to Go" is the title of Chapter 13, which is just trying to plant seeds for ideas that individuals can explore on their own (or that instructors might consider incorporating into their courses).
If you could provide a more specific reference to where Shimon is saying something like this, I will gladly take a look, but I am not aware of there ever being any plans to formally do a Part 3.