I question whether we really need the "https" scheme in IPP. It only tells a client to use HTTP/SSL on a default port of 443 (?), when connecting to the server at this URL.
We already have "printer-uri-supported" and "uri-security-supported", both as Printer attributes and in the SLP Printer Template. If a client wants to use SSL to communicate to a Printer, it can examine these two attributes and find the URL to connect to with SSL. There's no reason that the URL couldn't have an "ipp" scheme. Having an "https" scheme would add no information at this point; it is already given that this URL is for SSL. The client can get these attributes from SLP, or it could do a Get-Printer-Attributes on an unsecured channel to the Printer.
See the original message at http://www.egroups.com/list/ipp/?start=4875