Dealing with proliferation of package variants vs. ease of selection

Crossposting from https://github.com/conda/conda/issues/11053 because it affects conda-forge in many ways.

> More and more packages come in various different flavours, independently of relatively fixed things like the python version. A non-exhaustive list:
> - cpu vs cuda (vs. eventually ROCm or Metal)?
> - blas-flavour
> - mpi-flavour
> - openmp-enabled or not
> - possibly for CPU [arches](https://github.com/conda-forge/conda-forge.github.io/issues/1261)
> - builds for different licenses (links omitted)

I opened that issue on conda to find out if there might be a better solution than tacking on more and more things onto buildstrings. 😅