Discuss possible log-linear WCS handling in Spectrum1D

> Having `Spectrum1D.__init__` handle log-linear scales itself would perhaps be a nice feature, but definitely a new feature/enhancement, and thus warrant a different issue (and probably some discussion if it's worth the effort).

_Originally posted by @dhomeier in https://github.com/astropy/specutils/issues/832#issuecomment-877358133_

This issue is mostly to have an active issue logging the fact that there was potentially more discussion to be had about this case after closing #832.

Start with Spectrum1D.__init__ and the linked discussion in issue #832. Determine whether log-linear WCS handling belongs there and what behavior would be required; done means recording a clear decision and follow-up scope for the proposed enhancement.

Written by the indexing model from the issue text.