For releases 7.31 and 7.40 it is possible to create, in STRUST, PSEs with key length higher than 2048 bits.
One need to apply SAP note 1856192, executing the manual pre-implementation steps.
This is the result, after applying the note and patching the kernel:
As mentioned in the note, the limitation existed only in STRUST. Via sapgenpse a PSE could be created with key length > 2048 bits. One could then use SAP note 1178155 to save the PSE in STRUST.
I hope this helps,