You ask and we deliver. In the last version 0.3.0, we included the first draft of subgraph functionality. We called Subgraph a user custom node made by creating a graph with Inputs and Outputs nodes and exporting this graph as a subgraph.
Subgraphs can be shared or unique, shared subgraph is simply a subgraph in which changes are propagated to all of its clones, this is very handy while having a custom node multiple times in a project which you are still changing. A shared subgraph is simply created by copy-pasting any subgraph, the link is created on paste action.
But sometimes you want to create a unique copy of a subgraph, which won't be changed with others subgraphs. In this case, simply select your designated subgraph and click on the "Make unique" button, this will disconnect it from the other same subgraphs.