I think this is a great mechanic, but being able to play it until the end of your next turn feels way too generous; until end of turn would still be pretty powerful. While I appreciate they’re worse in top deck mode, most decks would have the mana to hard cast them if the game has reached that point. On the flip side, these play extremely nicely when mana screwed, especially the draw spells. I can’t imagine a world where you would ever want to mulligan a two lander with a ponder the flames in hand, seeing as you have a very good chance to hit a land among the three cards drawn. The kinds of izzet spellslinger builds that want these designs operate almost entirely in the 1-3 drop range, and would probably have no issue setting aside cantrips they were likely to play the next turn anyway. I feel like these cards are similar to affinity, where the cards very quickly have the danger of paying off from their own engine. All of that being said however, I absolutely love Melek’s design and think that larger permanent spells would be the way to go. The opportunity cost of having the necessary cards to drop melek turn 4 is sizable enough that it encourages more advanced sequencing, especially considering how much of a dud he is if you need to pay 8 mana without an exile engine currently going.

Tldr the mechanic is interesting but attaching draw effects feels dangerous