I have a board designed for a dual-die Micron MT25QL512 QSPI NOR flash. These parts are in short supply, but the board fabricator had some single-die MT25QL128, and used them instead. The single-die chip has the same footprint as the dual-die chip, but the pins for the second die are marked 'RFU' in the datasheet, with the note:
"Reserved by Micron for future device functionality and enhancement. Recommend that these be left floating. May be connected internally, but external connections will not affect operation."
Is there any risk in just leaving the weak pull-ups on the unused pins? (On the MCU I'll mux the pins to GPIO input).
UPDATE: It seems to be okay just to leave the pull-ups on the unused pins. I've been running for 3 weeks like that, without noticing anything strange.