Hello,
The same situation is with libssl1.1/libssl1.0 [1].
I would recommend to follow its way, to avoid pitfalls:
src:libewf/20140606-7, stripped-down:
- libewf2-dev
- libewf2
src:libewf3/20171104-2, new package for unstable:
- libewf-dev (Conflicts: libewf2-dev, without Replaces)
- libewf3
- ewf-tools
- python-libewf
- python3-libewf
So, when we drop libewf2, the package libewf-dev will not be renamed.