Brianna, apparently your contact mentioned DNG, but
the excerpt you
quoted only mentions "higher resolution files". 300dpi JPEG files are
not "just good enough". They're high resolution files. Now, if we want
to follow the standard of the printing industry, the priority would be
to allow TIFF files.
Afaict it is rare for a photographic TIFF to contain more information
than can be stored exactly in a PNG. PNG is a much saner format than
TIFF for a project like commons.
What we do need though is the ability to choose thumbnail parameters
other than size. e.g. have a png in storage but generate JPEG thumbnails
from it.