Prove it. Prove that i5 is faster than the quad core Ryzens.
Every serious independent benchmarker out there has already done so. Ryzen IPC is 11% slower than Intel 4th Gen, on average, clock for clock. Then you take clockspeed for particular model of chip into account, and whether it can be overclocked. Look it up.
Then you have the new Coffee Lake i3 quad core, which spanks the Ryzen 1200 even more.
He doesn't have to buy an old and dead platform without any future upgrade path.
Like I already said, he doesn't. But you keep going on about upgrading and ignore that i5-4690 + 1050Ti is faster than 1200 + 560 right from the get go which makes it better bang for buck. He wouldn't have to wait to upgrade for better performance.
Also, unless he's thinking of upgrading very soon to a six or eight core, by the time he does so it would be pointless as Ryzen IPC would be far behind newer platforms. You'd get the cores but not the single core strength (compared to newer processors by then) that plenty of applications/games make use of. It remains to be seen how much AMD can improve IPC in future AM4 iterations.
In summary, he should go for a Ryzen build if he plans on upgrading processor within a couple of years. If he'd rather just get the best for his money now, and a 1050Ti, then i5-4XXX is a good option.