I agree the opportunity is still there, although the long game keeps getting longer.
Prof. Viktor Leis suggested [0] that SQL itself - being so complex to implement and so ineffectively standardized - may be the biggest inhibitor to faster experimentation in the field of database startups. It's a shame there's no clear path to solving that problem directly.
Absolutely agree! On the bright side, widespread adoption of Python-like general-purpose languages gives me hope, that similar options will multiply in the DBMS space.