I also wonder will the 3400g beat 9400?
Probably not. It might clock a little higher, but IPC will also be a little lower, being only Zen+. It will probably be pretty close, but will likely fall slightly behind in things like games. The real advantage for the 3400G will be its superior integrated graphics, for those making use of them. If you plan on using a dedicated card though, it doesn't make much sense, since you can already get a Ryzen 2600 for about the same price, with 50% more cores and threads, which should be overclockable to a similar level. Or the 2600X for just a little more, to get those higher clocks out of the box. Or for just a little more still, a 3600 with improved IPC that might perform more like an i7.
Another thing to consider is that until B550 motherbards are released, it might be a bit tricky to find boards guaranteed to ship with a BIOS that supports the new processors out of the box, unless you go with X570. Those boards will undoubtedly be priced higher than B450 and probably many X470 options, so unless you have a first or second gen Ryzen processor on hand, a 3400G build with a dedicated graphics card might end up costing more than a 2600X build, at least until the mid-range boards come out.
Actually we're currently at 6 cores being the minimum for gaming as some newer modern titles get bottleneck by the 4 core i5 7600k and getting beaten by the ryzen 1600 which has less clock speed and IPC. So having 8 cores to give a little more headroom for multitasking or streaming is a good thing. In the future we may see 8 core utilization.
The SMT will likely help as well. Six cores without SMT is arguably a good current minimum for ideal performance in some of the more demanding games, and the current i5s generally perform well in these titles. The Hyperthreaded quad-core i7s also hold up pretty well though. So, a 6-core processor with SMT should similarly provide some headroom for future, more heavily threaded games. I don't suspect many game developers will be utilizing more threads than a 6-core, 12-thread processor can easily handle for a number of years, so that could arguably be considered the current sweet-spot, at least if one isn't streaming or otherwise heavily multitasking while gaming.
I am personally waiting for NVDIMMs to become more common for mainstream as I feel storage is the largest bottleneck on systems today.
Eh, I'm not sure I'd say that. Or at least, the vast majority of current applications can only benefit so much from additional storage performance. Just look at game or application load times, and how little they are affected by moving from a SATA SSD to an NVMe SSD that is theoretically multiple times as fast. You might get around 10% faster performance, or in many cases even less than that. Applications are still widely designed with hard drives in mind, and most will probably be for many years to come. Any frequently accessed data is typically held in memory, so application performance tends to not be affected all that much by storage performance, aside from situations where the files in question are too large to remain in RAM.
Also the video didn't show min FPS. It was Average FPS with the 1% frame time as the dark blue bar.
1% lows are effectively a better way of looking at minimums. They are the result of averaging the lowest 1% of frames, so you don't have a single frame throwing off the numbers from one run to the next, nor do you have frequent stutters getting hidden by the rest of the frames around them, which can provide a better representation of how smooth a game runs.