I’ve always done silver/white for my iOS devices when available - it gives them some aesthetic charm as being Apple devices going back to the iPod days, plus dark grey/black seems to be the default for almost every other device on the market.
But now that iOS devices seem to be moving towards minimalist bezels and OLED screens, the bezels that remain are understandably black to better blend into the screen. I imagine white bezels aren’t going to be around for the long haul.
I’ll probably try dark mode nonetheless when I install iOS 13.
I wouldn't have thought this would be an issue for those who like white bezels. Always just assumed that they liked the light colored interface to the point that if given the option to enable dark mode they'd just opt out.