What’s a niche/theme that deserves its own ETF, but still doesn’t have a good one?

What’s a niche industry, emerging trend, or overlooked long-term theme that you think deserves its own ETF, but still doesn’t really have a good one yet? Not broad categories like AI or cybersecurity, but more specific ideas that feel underrepresented, overly diluted, or poorly captured by existing ETFs currently on the market. Curious what themes people think still have a gap for a truly focused ETF product.