I do this with two ps4's and my son. 

I originally got two ps4's because I read MS wasn't going to allow this after the family pack being discontinued. 

However, I know someone who does it and I believe he said it works the same as on ps4. 

You buy the digital title once to be shared.  Child plays on main x1 since gold can be shared (much like psn sub account) adult or owner logs into secondary as oneself.  The primary has to be the one the child, gold sharing (I.e. Psn sub account S similarity) and secondary is used by digital owner. 

I don't own two X1's I've never checked but see if it states games can be used concurrently by up to two individuals as PSN states. 

I hope it works for you. I do this with my son and we play together and it's great since split screen went the way of the dinosaur. 

Yep me and my nephew do this on Xbox One. I purchase the games and he has them. He has my very 1st and main Xbox and I have my 2nd one I bought.  

Don't you mean the I have 23 ps3s guy

Do you do it in the same household?

I do it with my son in the same household just in case it is watched in someway.  The only game I have ever encountered an issue with was ESO.  The main game is allowed to be shared but the DLC is not.  I found out the hard way through a phone call to PSN.  It is ultimately up to the publisher/dev.  There might be others but that has been the only one I have personally found.

Other than that it is a great feature.  Especially, like I said, considering split screen is so often not an option it seems.