When we originally marked this issue as completed we did not take into consideration the ability to ignore certain tables in migrations for overlapping models.
This is still not supported in EF Core (or in EF6)Richard Beier commented
This would be useful for us. We have two systems which use different schemas in the same DB: a legacy system, and a new system that uses the legacy system. The new system is using EF code-first with migrations. We sometimes need to make modifications to the legacy system's schema... it would be nice to use migrations for that too.
Maybe it will work if we have two separate assemblies, one for new-system migrations and one for legacy migrations. But if the migrations are all tracked in the same __MigrationHistory table, I guess it's not currently possible to independently roll back or roll forward the changes to each schema.
Migration would be easier if we just used separate databases for the two systems. But that would increase the maintenance overhead, and I don't think our DBA would like it.