Hi
It is worded as biotech but may as well be molecular computing or nanotech.
biotech machines tend to be inaccurate, but highly parallel. Unfortunately the G machine is very un-parallel and requires 100% precision. Things like speculative evaluation may be more interesting.
To add garbage collection, roots send out a periodic (or sustained) signal to all connected nodes. Nodes receiving the signal do not self-destruct. Nodes not receiving the signal invokes their built-in self-destruct mechanism to dissolve themselves back into nutrients. There may be better schemes.
I think that in a novel machine you aren't going to want to do the traditional methods of garbage collection, or anything else. You'll probably need entirely new methods of doing entirely new things.
Debugging can be done by making evaluators send radio signals concerning operations they perform; then a second computer can log these and you can review them. You can also use radio signals to instruct the evaluators to perform unusual operations on demand.
It would also be a shame if for the G'-machine we have excellent debugging capabilities, but for normal Haskell on a normal computer we're stuck with Debug.Trace... Thanks Neil