ISubscriptionClient is absolutely the wrong place for this functionality. That interface is all about registering resource providers for a subscription with RDFE. All the other code (which was already being done in this cmdlet, I just rearranged it) is about the current and default subscriptions, and updating the local subscriptions file. Totally different concern.

If I had to guess, I'd say that functionality actually belongs in either the GlobalComponents or SubscriptionManager classes.