TL;DR: I'm looking for new people to resume work on sandbox, and I will
most likely branch it at v2.10 and start keep-alive work on top of that.
The state of our sandbox is not very well. Gentoo is currently using
the old v2.10 with local patches. v2.11 is p.masked for a long time
because of multiple unsolved bugs. The git repository also includes
v2.12 tag that has not even been packaged for Gentoo. From what I've
been able to establish, the bugs causing v2.11 mask are still present
in git head.
To add to this, the only person maintaining the code (vapier) has not
touched it since March, and AFAIA he's not responding to any contact
attempts from within Gentoo. Given this and the importance of sandbox to
Gentoo at the moment, I think it's reasonable to presume he's MIA
and start looking for volunteers to join the effort.
I have already added myself to the project page  and I'm going to try
to put some effort into improving the state of things. However, I'm not
really an expert in the high magic used in sandbox. If anyone is
interested in helping out, feel free to add yourself as well.
The above considered, I don't think I'm really going to be able to solve
the problems introduced by v2.11. If nobody has a better idea, I'm going
to branch sandbox at v2.10 and look into backporting whatever's feasible
and resuming development in hotfix mode on top of that.
In other words, don't expect any major developments. Only minor bugfixes
and whatever is necessary to keep the project semi-alive before we
deploy a suitable replacement.
By the way, if anybody is interested in a side Portage project, I've
added sys-apps/sydbox a few days ago and it's waiting for proper
integration into Portage. It's very neat but might be a bit hard to
figure out at first, so I can be of help with that.