A key thing to understand about “full support” is that many Processing-ecosystem libraries won’t ever be available on p5 for python, as they are Java-based libraries. If you want that, use Python mode (Processing.py) which is Processing 2.7 on Jython.
For p5, “full support” might not be a goal, given how big the Processing (Java) API is and the fact that some parts of it don’t make sense to duplicate in Python. For example, they might decide not to replicate loadTable because Python already has a great built-in csv library. p5.js has followed a similar path – they don’t implement absolutely everything from the Java API, and some things they may never implement.
I’m not sure whether this is a timeline, but you might ask @abhikpal or leave a question here: