Na... Just means that when banks etc consider that the critical mass of devices with keymaster 3+ / Android 8+ is sufficient to justify enforcing strongIntegrity in combination with a consideration of the number of modern devices (OnePlus and others) that still have broken keymaster implementations and can't pass stongIntegrity verdict, they'll adopt that option and running such bank apps etc will be out of the question for any device with an unlocked bootloader as it will be for older (A7 and earlier) devices and many (notably OnePlus but also some RealMe, Xiaomi, other) devices with busted OEM keymaster...
FWIW, I believe this decision is still a way ahead as banks will be hard pressed to make the move with this known casualty list... Further, I don't imagine Google will preempt this move either, but I think they'll be obliged to move to adopt strongIntegrity for G Pay, Playstore etc once banks do... I now believe they're waiting just like we are... This is only a hunch but...
So custom ROMs themselves are in no danger...
Eventually it seems you may also need to carry an unmodified phone in your other pocket if you wish to have a customised device as a daily driver...
PW