1) I like the RAM idea and in general more storage adapters. I hadn't really thought of local storage, but it makes sense for super simple prototyping.

2) I want to add DB profiling at some point (right now Libphutil does this for me at a query level, but I want to do it at a graph abstraction level). History could presumably be similar to a permanent profiler.

I think constraints vs flexibility is always a tradeoff. The main benefit of this model is very rapid prototyping where design decisions can be changed or reversed with minimum effort.