Thanks for the perspective and input. I very briefly considered going the Ryzen route, but have been very skittish as I've been in the Intel ecosystem for basically a decade now. Haven't built a PC with an AMD chip inside of it since I was in my teens.
She's going to want to play games at 60fps @ 1080p. Stream quality isn't imperative for her, but she'll want her streams to at least look good. Might go the 30fps route when it comes to streaming if it means a better looking stream.
But, back to Ryzen. I looked at benchmarks, and like you've said yourself, comparable Intel CPU's outperform their Ryzen counterparts in basically all game applications, with Ryzen outperforming Intel in basically all other use-cases. I feel like we've been waiting for games to really take full advantage of quad and hexa core processors for 5+ years now, and I'm worried about putting my eggs in the Ryzen basket purely on the hope that future games will start taking advantage of what Ryzen does best.
I'm also, like I said, a little skittish about doing an AMD build, as I just have zero experience with any modern AMD products. I don't know the quirks and specifics of that ecosystem and would be afraid of making mistakes with motherboard and RAM choices.
I understand your hesitation, especially with the concept of gambling on the future.
For what it's worth, some games have already received optimizations for Ryzen CPUs like Dota 2, Rise of the Tomb Raider and Ashes of the Singularity.
Although I wouldn't expect many games that have already released to receive optimizations, unless they're being constantly updated like Dota 2 is.
Games have been taking advantage of 4+ cores/threads in CPUs, especially Intel CPUs although perhaps not fully.
Interestingly Ryzen's gaming performance is a bit odd considering the CPU power that is available, it seems optimizations need to be geared towards the CPUs themselves, not just the number of cores/threads they have which is why some games got optimizations for those CPUs.
Here are some examples of the CPU core scaling that can be seen on Intel CPUs.
Battlefield 1
Source - PC Games Hardware
Assassin's Creed Syndicate
Source (PC Games Hardware)
In Digital Foundry's testing you can see the i7 7700K distancing itself from the i7 7600K.
Digital Foundry - i7 7700K Review
Unfortunately I can't say for certain how Ryzen's gaming performance will be in the future, the best thing to work with is the performance we can see now and the gaming performance of today shows that the i5 7600K outperforms the Ryzen CPUs in the majority of games, however
they both appear to be capable of delivering 60 fps in most games, even with the 1600x being underutilized.
I guess you have to decide if you're happy with it's performance in today's games, if you are then performance gains in the future as it is better utilized would be a plus.
I'm not sure if you've already seen this but Paul runs some benchmarks and his video provides a pretty good look at the performance of the Ryzen 5 CPUs against the 7600K.
RYZEN 5 REVIEW! 1500X + 1600X Gaming Benchmarks vs 7600K - Paul's Hardware