As of right now, bonding/pairing features with ESP-32/NimBLE Bluetooth stack for Micropython are non-functional. Any attempt to pair allows the device to temporarily pair but no interrupts are actually called. This includes the interrupts with data for password/pin bonding and passkey transfers, making a permanent (repeatable) connection with an ESP-32 impossible. The docs do confirm that this particular feature is non-functional on ESP-32.
I don't believe this function would take up much additional on-board resources and would greatly improve the use of the already-existing Bluetooth library. I feel without this function many users simply would not use the entire library, as it is a fairly important part of Bluetooth and enables many very common and practical uses such as L2CAP and native use without code running client-side.