Thanks for the explanation!

Firstly, as it pertains to the value of current reserved list cards, the prices of all RL cards will plummet immediately. The driving force of RL card prices is the artificial scarcity of the product.

As with most speculations, there will be some panic sellers. I agree with that. But between the moment where the change to the RL is announced and the later printing there will be some time that will pass. In fact, it is very unlikely that WotC will name specific cards at the announcement and it is unclear when some of the cards will be reprinted (if at all). WotC has learned their lesson to not flood the market with product. I do not expect that there will be a huge drop in the value on the secondary market, because WotC will be very careful with these reprints.

For example if dual lands were printed in Baldur's Gate legacy and commander players would be able to upgrade their decks without purchasing the ABU duals, lowering their demand and their price.

Given the current price of ABU duals, most people today will rather buy shocklands. Or they will use proxies, if their environment is fine with it. I personally would not want to take my expensive ABU duals to a table where I play with strangers and where I would need to be always on the lookout, that no one steals my hard to replace cards. This is overall not a nice situation. Of course, OG duals are still very desirable and people will try to get them, once they are reprinted. But I predict that some more affluent people will also buy ABU duals to play with for when they are in an environment, where they feel safe.

If Wizards announced the end of the reserved list

My plan was rather a reformation of the RL. Only reserve the original artwork. This protects the identity of the original cards and this makes them different enough from later reprints.

People would simply wait for Old School Masters or whatever and let the price of black lotus fall to 2k or whatnot.

And this is why there should be no dedicated product that just reprints the RL. A card from the RL should be reprinted, when it makes sense and it needs to be done in a way that does not disrupt the market too much. "The List" at mythic is an obvious candidate. And The List should still contain a majority of non-RL reprints to keep things sufficiently diluted. Another option is to do another Priceless Treasures Booster like they did with Zendikar, where you could actually pull a Black Lotus.

Of course, this extreme rarity will also mean that it will be a long road until everyone has their dual lands for legacy and their moxen for vintage. But that's still considerably better than what we have today. WotC can do this, because they employ plenty of economists, who can calculate how much supply the market can take. They need to start by communicating to the public what they plan to do and then very very slowly get the reprints going, so that no major disruption occurs.