There are moderators and members here who are playing AAA games using 980ti's, 1070's and 1080's running both Sandy and Ivy, and do not feel like they are seeing a reason EVEN NOW to really update their CPUs. Obviously, a newer CPU would perform better, but the fact remains that even with what he currently has his i5 will probably be fine with anything from a 750 ti all the way up to a 1070. Especially if he is running a high resolution at fairly high settings, which will take a lot of the strain off of the CPU.
Truthfully though, a 1050ti is probably more than enough if he's running a 1080p or lower display. A 1060 as you say would allow a bit more eye candy. If he plans to upgrade the CPU and motherboard at some point, I would totally not be against any card he chose to install all the way up to a 1080ti though. It's not going to perform up to full capability, but if he upgrades later the practically any card he chooses now is a good choice and will be miles better than what he's currently rocking.