I’m not super plugged into scala but I work with Spark quite a bit and my observation has been the whole scala 2.13 -> 3 transition is a huge mess for just about everyone who touches it. I don’t have enough hands-on context to understand why it’s so painful but it seems to be similar or worse to the python 2.7 -> 3 transition in terms of sticking friction.
It is a mess. I've spent some time trying to convert some academic oss projects and some removed features really force large redesigns. I think rather than funding the stuff on this announcement, I wish they would fund a team of experts to work on migration of a prioritized list of projects. This would both provide example patterns of migrating substantial projects and unblock projects who have been saying "we would like to try migrating but library X we use still hasn't"