advices needed related to the major change of content moderation entities planned for 8.3

As you know Content Moderation is an experimental module, and therefore is subject to change and has no upgrade path.

In this case a lot of Content Moderation has been abstracted into Workflows module. So as long as the moderation states you have in Workflows module match the moderation states you had in Content Moderation then the upgrade path should be pretty straightforward.

I've not tried upgrading from 8.2.x to 8.3.x but I suspect the biggest issue you'd hit is that the moderation_state field defined in \Drupal\content_moderation\Entity\ContentModerationState::baseFieldDefinitions is now a string field and not an entity reference field.

If you can get a full or partial upgrade working it'd be interesting to add it as an update hook in Content Moderation for 8.3.x

I have explored and briefly started writing this upgrade path and will be eventually have to write a partial upgrade path for a project which is in production using the 2.x branch. For the content entity which stores the moderation information, that will definitely require an a scripted update if you have a large number of entities, no getting around that. There are also a few major config changes that will need to happen. First and foremost the workflow/state/transition config objects but also any views that create relationships/filters on the moderation states. I'm thinking these will be handled manually in my case. Then obviously any custom code built around workflows will need testing and adjusting.

Those are the biggies I've scoped out so far, but I luckily have a really thorough test suite to inform the process when we eventually have to get on to 3.x.

Adding the upgrade path issue as related.