5 is introducing the aspnet50 and aspnetcore50 platforms. net45 support implicitly gives aspnet50 support so nothing is needed there. There is a temporary policy that allows win81 to implicitly give aspnetcore50 support, but that will be removed in the near future (as the platforms aren't actually the same - just very close).
The existing package works just fine on aspnetcore50, so no code changes are required.
aspnetcore50 has not shipped in an RTM release yet... so you probably only want to publish a pre-release package with support in case the name changes in the future.
Let me know if you need more info.