From my faint memory: When UniSwap v3 launched, I remember it was perceived more as an alternative to v2, not a successor. One reason was that the concept of "concentrated liquidity" wasn't useful for everybody. I remember us discussing that many projects & people kept their liquidity on UniSwap v2 (initially? did it ever change?).
How do we feel about UniSwap v4? Will it lead to another substantial split of liquidity? Do we even care, or are trades with the v2/v3/v4 pools routed through the same interface anyway?