The OP is likely not running a Z series motherboard, so they're going to be limited to DDR4 2133 anyway. In that situation it probably doesn't matter if it's Intel or Ryzen "ready". I personally don't see it as a waste of money to buy a 2x8GB kit to use on the current system, before getting the rest of the new upgrade parts, unless the OP's motherboard is using DDR3. I suppose one reason not to buy the ram before the rest of the parts is if you're worried the ram will have a compatibility issue with the new AMD motherboard such as not running at advertised frequency or timings and you can't check that with the current system because it can't overclock ram.
AMD has a list of memory kits compatible with Ryzen that you can check against when searching for ram.
https://www.amd.com/en/processors/ryzen-compatible-memory. My Patriot Viper Steel Series DDR4-4000, which were intended for Intel platforms, are not listed as compatible on either list, but I'm running two of those 2x8GB kits at 3000MT/s CL14 on my Ryzen 5 2600 with my B450 motherboard.