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.
Dot com was a bubble because you could call your company anything with a "dot com" on the end and get funding for it without a business strategy. Indie games never got that treatment.
And without the investment angle, there's no bubble.
A bubble isn't "they're really popular right now, and there's a whole bunch of them popping up". That's a fad. A trend.
A bubble is always in reference to investments. It's a pump-and-dump scheme at the level of the whole economy. The housing bubble isn't because there's a glut of houses on the market, it's because people are trying to market houses as an investment opportunity for market squatters and landlords.
And yet some of my favorite indie games are games practically nobody's ever heard of. Most recent was Metal Unit, a game that I don't know how I have in my Steam library and somehow evades the internet's favorite rule despite the main character being an anime girl in a bodysuit. At time of writing there are 17 players in-game.
So while good games are good and bad games are bad, the good ones may not necessarily be sustainable.