RIPs should consume XPS natively I'm mailing with someone who has trouble getting his XPS data printed on their digital presses. The RIPs cannot handle the XPS format, and so the customer needs to convert the files to PS via driver sofware, leading to gigantic PS files and more troubles down the flow.

It shouldn't be like that.

XPS is a perfectly fine format for a RIP to take in, it's well specified, and any conversion to an intermediate format like PS is bound to introduce trouble (huge files, slow performance, rendering issues, etc...).

Good to read the EFI has included native support for XPS in the new release of their Micropress RIP, used in a lot of devices on the market (link to brochure).  ¶ 12:38