Is it possible one manufacturer "takes the leap" and provides ram modules that are faster than competition. Therefore driving the transition purely on competition alone?
Doubtful. PCIe Gen 5.0 x16 over DDR5 is a huge cost increase, a huge latency increase, and only a minor bandwidth increase (about double after accounting for protocol overhead.) At that point, you might as well widen your memory bus and use 2 DRAMs. The memory controller doesn't get much more complicated because both chips share a CA bus, and the DRAMs are cheaper. I don't work for a DRAM vendor, but I would imagine that the front end logic in the DRAM (the DDR controller inside the DRAM) uses way less than half the die area that a PCIe Gen 5.0 x16 EP would use.
No, because they're in an unspoken, totally not illegal oligopoly not to dump prices.