Here's an updated picture:
You can see 7 pin SIL rows for the displays and the six switches/encoder (two positions possible). Encoders with built-in switches are supported but you have to wire your own pins.
Possible configs are:
OLED OLED OLED OLED
OLED [6 buttons] OLED
OLED OLED encoder
OLED [6 buttons] encoder
only switches
only encoder
combo of switches + encoder
fewer OLEDs
Pinning for the OLEDs is based off J15A from the Core32F4, same for the display driver.
Pinning for the SCS is the standard J10(A).
It would be possible to split the SCS functions across two boards, e.g. with OLED [buttons] OLED on one and OLED OLED encoder on the other.