I've been dealing with this issue for a couple of months now. On my SP3 at least - you should't have to do a full battery drain! A hard power cycle/restart should work. While the laptop is running, press and hold the power and volume up buttons until it cuts power. Continue holding as the device reboots. At which point it will take you into the Firmware BIOS. From there you should notice your keyboard works. So just exit firmware via the menus and windows will begin to boot. Viola! Working keyboard. At least until the next restart/sleep.
As a work around I've disabled connected standby and set up a power plan to prevent the laptop from going to sleep. Not ideal, but at least it's usable. It only takes a few extra seconds to get into a session with a working keyboard. Yes MS should fix this ASAP.
The key to this is that you have to ensure that the battery is COMPLETELY drained. After you leave it on until it dies, push the power button until the low battery icon doesn't show up anymore. After the low battery button icon doesn't show up you need to leave it unplugged for a couple more days.