Old new like from July 
"You can visit your friend's house, you can log into your account and play any game from your digital library," - http://www.officialplaystationmagazine.co.uk/2013/07/10/ps4s-digital-library-lets-you-play-your-games-anywhere-on-anyones-console/
And I guess you can install and play with other account... just that the master account have to be registed in the other PS4 and online (you know the PS4 can have 4 accounts online at the same time).
So it is how I guess it works...
1. You buy a game with Account1
2. Donwload and install in PS4A
3. Play it with the master account in PS4A
4. Download and install in PS4B using the Account1
5. Use the Account2 to play in PS4B but the Account1 was logged on background
The PS4B will automatictly to log in in background with the Account1 to see if you can play the game... and the numbers os PS4 you can have the game installed is infinite.
The big question is... if I'm online in PS4A with Account1 then I can be online in background in PS4B to play the game? I can have the same account logged on two PS4 at the same time?
If not then you will can play the game in other PS4 just when the Account1 is not online in any other PS4.
I guess you can't play the game while it is running in another PS4... so you only can play the game in one PS4 at time.
Seems fine to me while the PS4 Master Account can be offline to play the game 
