>The language itself not much. It doesn't offer anything new that Java 1.0 with Quasar doesn't already have.
It offers lots of abstractions Java didn't/doesn't:
Lots of concurrency features, Ad hoc interfaces, Closures, Stack resizing, Type switches, Multiple returned values, Slices.
I too want 3.3+ support but I know some claim that there's very little demand from people actually doing something with PyPy for Python 3 support. I really think it may be a chicken and egg problem: that is, support will generate demand.
In any case the 3.3 branch seemed good when I compiled it last, it'd be nice to see a partial release.
ARC languages are Turing complete, but some algorithms require more than just "peppering weakrefs" and actually require you to essentially build your own GC.
Consider a graph which can have nodes added, and edges added or removed. Say you want to keep track of the part of the graph that is connected to a node.
You can't know ahead of time which references can be weak. So all must be strong and you will leak memory when a circular part of the graph becomes disconnected.
In general, garbage collection is a difficult problem that solves a lot. You can't trivially do without it. It's not just a tool of laziness.
ARC won't work when you cannot determine ahead of time where the cycle can end safely. Pretty sure for an interesting set of algorithms this is a problem.
It's something I find annoying about some ARC/Rust enthusiasts: their belief that because they haven't found need for a GC, that there isn't one.
"Thus, while our proof of RH might look too short to be true, it really involves at least two rather long papers [6, 8], not to mention [9]."