I could never justify the expense of the Threadripper series, because they require expensive motherboards and CPU coolers. I would recommend the 5900X CPU at this time, because I think I've seen price reductions and the motherboards are not that expensive if you don't require all the bells and whistles. Video card wise, keep your 6900 and wait until new cards come out this fall, or at least until prices fall over the summer for the existing video cards. Assuming you like the RGB parts (I sure do), I would go for 64 GB of DDR4 RAM from Corsair I think.
Maybe my situation is different from most, but I don't upgrade my existing machines much - maybe a more powerful video card or swapping an HDD system drive for an SSD system drive. Once I build a machine, it generally stays that way. I then build new machines so I don't have too many used parts that just sit around. When I decommission a machine, such as several old AMD Thunderbird builds, I turn to running Linux on them or eventually they become spare parts for other people that can't find a replacement for their old computer builds.
Why not create something unique, in terms of the case design? Modding is my hobby really - fitting computer components into old appliances like microwave ovens, printers, scanners and things of this nature. It's fun and creative at the same time.
As Albert Einstein said, "I could have done so much more with a Big Al's Computer!".
