Don't microcontrllers feature lockout so the internal code cannot be read and/or re-blasted?
Often, yes. I don't know about these particular ones but I wouldn't bet against it.
Could be a new hobby.. hacking decoders to upgrade the firmware.
Although the returns would be limited. With the V5, the Select is going away so there won't be any to upgrade there and the "Essential Sound Unit" is not available to the public - only to OEM's like Walthers and Scaletrains so you'd have to become a manufacturer in order to get them and if they then ended up on the black market I'm sure ESU would come down hard on you.