Honestly, what does $BTC and cryptocurrencies generally need to get into mainstream? Have you ever wondered before?
1. Bitcoin must step outside of its 4 year cycle. Nobody wants to hold such asset which drops by 50-90% after the end of cycle.
That's why almost no current ETF will survive by 2025.
2. Another cryptocurrencies should not be only copy-cat Bitcoin growth/drops.
3. Be less volatile or at least with rising trend which is not slave Bitcoin halving.
Alternatively, the question is not what Bitcoin needs to become mainstream - as soon as Bitcoin becomes mainstream, the 4 year halving cycle might be abondoned in the favour of stock market scheme..