No, RAM is not something that is exposed on the PCIe bus (which is what thunderbolt is based on). RAM has a different protocol (DDR5 in this case), and as it says in the article, is very sensitive to the distance between the CPU and the RAM. External RAM isn't really something that is viable in the modern era of computers as far as I know.
Surprisingly this is something starting to show up in the server market lately with a new protocol/tech called CXL. But yea that latency issue is still there over the distance but it'll let more remote memory type stuff start to happen. I doubt you'll do more than a few meters (i.e. within the same rack) ever but it'll likely end up getting used for so called "hyperscaler" type companies to more flexibly allocate resources, similar to how they're doing PCIe over ethernet with DPU devices right now. Unlikely that this will end up at the consumer level anytime even medium term because that kind of flexibility is still just so niche but we might see some CXL connectivity eventually for things like GPUs or other accelerators to have more memory or share better between host and accelerator.
Only CXL has the potential to be outsourced to Thunderbolt, as it works off PCIe and system RAM does not. CXL (Compute eXpress Link) is a server grade technology that's really aimed at solving some problems within the high performance compute area, like cache coherency. If you don't get it, I don't either tbh.