the entire system is set up such that value is supposed to go to the SPS token and from there it filters down into all of the other assets. For example, more demand for cards does not lead to more demand for SPS, but more demand for SPS will lead to more demand for cards (as cards are one of the primary ways to earn SPS in the game)

I don't actually think the value of SPS is that much correlated to the value of cards. SPS pumped to 3 or 5 cents months ago (can't remember) and the price of cards did not go up at all. Card prices kept going down. SPS is too volatile for it to factor into the decision of whether to buy cards or packs.

This proposal might end up in more people (old players) quitting the game rather than pushing more people to try Modern. That's my guess anyways.