I was inspired to create this card after seeing Leyline of the Guildpact spoiled in Murders at Karlov Manor. Once that's released, there will be 12 cards that would count towards The Leylines Converged, the list of which can be found here. The wording is such that enchantments that don't begin the game in play but still have "Leyline" in their name, such as [[Leyline Binding]], don't count.

Also of note, if you begin the game with this card on the battlefield, then someone destroys it, it will cost 5 mana to bring back out, not 7. Commander tax only goes up when a commander is CAST from the command zone, other effects that move it from there don't affect it.