How can /foo be accessed with content-negotiation such that they physically map to corresponding files /foo.html , /foo.ttl etc. Is the mapping something that Solid already provides (or could provide) or is that out of scope?
If this is missing, I think it is an important enough feature to have. if for example, /foo is described like: /foo dcterms:hasFormat /foo.ttl . /foo.ttl a dcterms:MediaType ; rdfs:label "text/turtle" . and so on, Solid can silently do the rewriting and give the corresponding response. Something along these lines could give way to having cool URIs
I think one thing we need to look closer is how do we (humans) or a solid server does the mapping. One way to do it may be for solid servers to automatically respond to requests for paths which have a "well known" extension, i.e., foo.ttl, foo.html, foo.rdf exists, and so /foo will do the rewriting to one of those based on conneg.