I am sure they will appear over not too long in some of the BTS modpacks (Water will not work tho).
It's everything king of a grey zone.
My understanding is, that it might be OK to use some of the Assets as part of a mod. Has been done with assets from other games - but technically it's just good will on the side of Firaxis to not prosecute it.
Just releasing the Assets on they own, might be a step too far.