Wrong question, in my humble opinion. A bubble is speculative at its core. It’s about traders, the stock market, investors, speculators and shit placing much more value on a thing than what it’s worth. The distance with reality grows massive, until everybody wakes up and "pop!" all that sweet sweet wealth (or savings, for the peasants) vanished into thin air. Think housing market or beanie babies.
The question here is if indie game dev can remain sustainable. It’s like restaurants: the more there are, the harder it gets. The risk is not nearly as sudden and explosive as a bubble though. If there are too many, some shops close, others shrink.
Furthermore, the tools and knowledge required for gamedev keep getting more readily available. It’s an art too, so there will always be someone somewhere with the overwhelming drive to do it, profitability be damned.