I don't get the skepticism. It's not even as if you guys are taking a measured look at it and deciding it's just not quite right for the 6 drop slot. Your arguments appear to be:
1. Six drops in MUD must win the game on their own and this does not; and
2. This is inferior to Memory Jar.
This isn't any different from how a blue player evaluates prospective cards:
1. If it costs 4+ mana it must have a huge impact if not outright win the game.
2. It must not be inferior to any playable analogs.
3. It must fit in with a prospective deck's game plan.
This card 1) costs more than 4+ mana, but likely has a large impact on the game at the cost of tying up turns doing little else besides drawing cards.
2) The investment required makes it difficult to to pinpoint if it is on par with cards like staff of nin or coersive portal, or even jar. There are already things that fill the draw options for shops, some of which don't get shut down by null rod.
3) As has been stated, this card becomes increasingly difficult to cast the later it gets drawn. Unfortunately the best time to utilize it is later in the game. In a typical shop deck it fights itself, something the analogs don't do.