Declining demand for 'traditional' RF lenses does not mean that the prices for those lenses will go down- quite the opposite. The facilities that design and build these things do not have the luxury of scaling back instantly with the market- they have skilled labour and high-cost facilities to maintain, whether they sell 1000, 100, or 10 lenses. In the short term, they will simply pass their overhead on as a price increase.
Combined with the other factors I mentioned, I don't expect any price decreases for new camera lenses. I expect substantial price increases.
This is the best buyer's market for used gear that we may ever see... enjoy it!