The continuous discussion rather fits into the other thread, but I’m going to reply here:
You are right that the value of extending licenses should not be to get just the same, well-maintained core product as before and everything else from extensions.
When developing software there exist these necessary efforts (like refactoring bad/old code, improving maintainability or build system or CI system) that serve rather the software producer, but are hard to sell to customers. Others are “nice to have” (beautiful Welcome dialog, although I must admit Recent Files is so good that I don’t disable the dialog for the first time anymore), and other awaited ones massively improve productivity (even if only users of some fields benefit and see the value). How can one balance all of these under the constraints of functionality, budget, quality and time?
What has become generally known is that not all planned features became ready to the (extended) deadline/release date. We can assume or hope that almost finished features would be included in the next release without taking away significant development resources for more new features planned for next release, meaning hopefully a compensating release 2020.
Isn’t it also quite remarkable that SketchUp for Web includes a native Solid Inspector tool although it has neither an extension API nor is this new Solid Inspector written in JavaScript (apart from its UI), but in C++? 
The outlook of subscriptions with a continuous flow of new features sounds kind of promising that features won’t anymore be delayed for a year due to fixed dates. This is good for both developers and users!