Apple's Private Relay is a cool and effective setup. It made me think about a system-wide alternative, hence the title. It could almost be a service in its own right, seperate from Proton VPN but included in the vpn interface for Plus/Ultimate subscribers. You could also build on top of that partnership for a tor alternative and bring Mullvad in as the middle node (vice-versa for users already using mullvad vpn). All three could have dedicated optimized servers for the service. "Mullton9" ? Lol. "Provad9" sounds too much like an ED med. Use-case would be someone who just wants privacy and speed. They would use original VPN app/service for all other uses (tor, p2p, different country, etc)

Make it a paid service. For proton users they have "Proton9" private relay and "Mullton9" tor alternative (mullvad is middle node). For mullvad users they have "Mullvad9" private relay and "Mullton9" tor alternative (proton is middle node). Quad9 is the egress server for all options. Would provide another income stream for all 3 and probably be pretty popular!