For some of my own work, I tried to find the electrical requirements/code that required the interlock switch. 70V DC is on the edge of what may or may not require that. With 48V DC there is no requirement.
I'm confused by the problem caused here. Without the 48V dropping when you open the coin door, you don't need anything special to keep the flipper coils powered ala "ball save". Or am I missing something?