You dont need to bounce the land, so its actually pretty reasonable as a way to punish people who dont want to play into your Torrential Gearhulk mana
Of course, Secret Lairs have had bonus cards for a while, but at first these were a fixed card everyone who bought the same lair was guaranteed to get, and not typically something super rare either
Hey, you can crack two treasures for a 50% chance to win one treasure
Sure, useful cards from this part of Magics history can and will spike in price, but Ive seen people worried about the supply of cards like Wall of Kelp
Medallions Current Price (via Card Kingdom): $11.99 $29.99 Every Medalion is getting a reprint in Commander Masters, so lets just lump them all together
You could also get some swirly effects to signify mana as well as doodads that look like Phyrexian and planeswalker symbols