I'm seeing many excellent used bikes with Di2 on eBay with rim brakes.
No way I'd go disc. Doesn't solve any problem. I'd buy one of these or similar used bikes and be happy forever:
https://www.ebay.com/itm/32522531894...wAAOSwtCZijmuw
https://www.ebay.com/itm/12539164088...UAAOSwiRhiu3NV