Know anybody, the reason, why no longer the easy and comfortable ANDing can be used and this irrational crossbar was needed ?
Some SILabs derivatives have more I/O functions than there are pins, this WOULD require a crossbar. When I started using Cygnal devices I hated the crossbar, now it is just part of a design.

I see only one solution, that I must select a bigger device and enable all potential needeed peripherals already at the beginning of the project.
Are you saying that when you design a project you do not know which peripherals you will need at design time?????. Also where is the difference? If you have a 'potential' need for !INT1, on a 'regular" devfice, you still can not use that pin for something else because if the "potential' need comes up, the pin must be free.

Erik