For powering down a mounted Mini-PCIe-Broadbandmodem it would be very useful to have a "powering switch" which is implemented on most 3G/4G-cards on PIN 1 as W_DISABLE#. Normally it's open (and pulled up to 3,3V) but with one short grounding you are able to fully restart the card.

This is a not implemented now as far as I know and so it's impossible to reset a non working device even with a router-reboot-script, because the card is always powered while rebooting. The only way to reset the card (now) is to manually plug power from router an reboot hard.

i would appreciate it very much!

I think it's not possible for old version of RB (ex. RB411U), and for new one (such RB912) you can execute /system routerboard usb power-reset duration=2s;