Perhaps the N&N guide can be enhance with a visual indicator what change is a breaking change?
I fear it's a bit tricky to identify what's a breaking change and what's not. We'd need more specific criteria for that.
Perhaps defaults can be changed more gracefully by only applying to new workspaces but not existing ones?
That would be quite frustrating for many users. Download stats of 2020-09 seems to show that ~1 million / ~25% of users run upgrades (and most likely use the same workspaces), and it's been recommended for a long time that people using a newer version of the IDE point it to the same workspace. So it could very well be that the vast majority of users keep the same workspace.
If we don't make default preference values changing on existing workspaces, we basically cannot deliver as many improvements to all those users.
Perhaps the migration guide/faq can be served more prominently (eg., cross-linking in N&N)?
That would be a good addition IMO. Can you please submit an enhancement of N&N to include such link?
On a side note, there seem to be some UI issues in the migration guide. Example: https://www.eclipse.org/eclipse/development/porting/eclipse_4_15_porting_guide.html ... click on the Platform migration guide prints out raw html instead of rendering it.
Can you please open a bug about that? Or maybe even directly submit a Gerrit patch to fix it?