So: early Monome modules (“trilogy” - WW, ES, MP) had a relatively high 5V draw, and not all Eurorack PSUs provided enough (any) 5V. ext5V was a way of not straining your Euro PSU, or providing meaty 5V if you didn’t have any spare.
Switch is a set of connections that make it easy to pass that 5V through to your grid, and also to easily swap one grid between two modules. Nothing more than that.
Ansible doesn’t require any 5V - this is on http://monome.org/docs/modular/ansible/ . (It generates its 5V from the 12V rails). Similarly, neither does Teletype, as http://monome.org/docs/modular/teletype/ states.
Correct me if I’m wrong.