I think some members are confusing terms, as in adolescence > maturity > dotting off to the nursing home. I reckon it’s fair to say that after 50+ years of constant development, DAC technology has reached “maturity”.
Dac technology has been largely worked out for 20+ years. For example, Vimak corporation who invented Delta Sigma technology implemented the only truly discrete Delta Sigma dac; the DS1800Mk1 released 25 years ago which was incredibly complex and over-built. Now, Delta Sigma dacs are implemented in miniaturized chips. And in the process I think they lost something actually.
But that doesn’t mean DAC technology is standing still, or that manufacturers aren’t innovating. Data Conversion Systems proprietary ring dac and APL Hifi’s proprietary DSD dac are good examples.