Drupal has everything to do with Community, the embodiment of vibrancy imbuing this Open Source project... so much so that the Community is justly touted as a factor differentiating it within the field of CMSs, and contribution to it is often used to measure a candidate's suitability for employment (a practice that makes sense on the surface but can be inherently biased).
Community is based on volunteerism, and while volunteerism is a great and noble thing with demonstrable successes, especially within the Drupal Community, there is a flip side to it: there is no accountability or surety, and that can be a large issue to the user community.
Let us consider the migration from D7 to D8. On the surface the process has come a long way, with the migration of fairly vanilla sites often being push-button. I posit that the problems, large costly and sometimes insurmountable problems, arise below that surface. One current glaring example is the Rules module, a top favorite in D7. It is still in alpha.
So, what about the multitude of sites that have a heavy investment in Rules, often as a result of their business needs being fulfilled by its use. There seems to be only a few choices for them of what to do, none of them pleasant or defensible, when looking in from the outside:
- Remain on D7
- Eliminate the need for the rule(s)
- Absorb the cost of converting the rules to custom code
Certainly the fact that there is no production D8 rules module, yet, is not a matter of fault. Module migration is like the tripod of any project: it comes down to resources, time and scope. That said, in a volunteer network the availability of resources is indeterminate.
We are now at the point of scheduling the arrival of D9 and the end-of-life of both D7 and D8, and still, there is a plethora of sites, enterprise sites, that make heavy use of Rules, or some other module not yet migrated, with a brick wall approaching and no brakes on the car.
At a minimum, I feel that mission-critical contributed modules and their migration need to be part of the release planning of a new version, rising to the level of blockers. We owe it to the clients whose use of Drupal means its success. After all, you can have "open source" music, but it means nothing if no one listens to it.