If you had unstripped-dev, now you would like them to Provide: the stripped -dev version, otherwise dpkg-buildpackage would refuse to build it. So the problem would be the same.
But, as I said, if packages in universe are build without multiverse (which sounds reasonable), I do not see the problem of having libxxx-unstripped packages in multiverse Provide: libxxx
If you had unstripped-dev, now you would like them to Provide: the stripped -dev version, otherwise dpkg-buildpackage would refuse to build it. So the problem would be the same.
But, as I said, if packages in universe are build without multiverse (which sounds reasonable), I do not see the problem of having libxxx-unstripped packages in multiverse Provide: libxxx