After some googling and asking around, I've not seen a similar description of what is happening to my MBP. I'm using a pretty new model (Early 2015 13" retina), and I have had no former problems with hardware.
2 days ago, I was using my Mac as per usual and after powering it up, my keyboard and trackpad were dysfunctional in the login screen. I just turned it off using SMC shutdown. It worked, and I rebooted only to have the same issue. Using an external mouse and keyboard work fine, but only Shift+Control+Option+Command+Power work. All other keyboard shortcuts don't.
I'm honestly have no idea what's wrong with it. I can give any extra information that might be helpful.