First commit of OxiPNG was 2015-12-15. The way I read the part you quoted is that they originally assumed OptiPNG to be dead, not that they are saying now that it's dead.
Absolutely agree with your point about reaching a stage where not so many big changes are necessary though.
Version 0.7.6 of OptiPNG was released 2016-apr-03.
Not super recent, but it seems reasonable, given the limited scope, that it would stabilize and not change much after a certain point