I used to think the Chuuren Poto was the only 9-way wait, but there's actually two more shapes.
7gate:
waits on

(

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8gate:

waits on

(

)
OR
waits on

(

)
Both waits wait on every tile in the suit, but they aren't fully nine way because there's 4 of one or two tiles already. If a 5th one came via haku pocchi or goumoupai, it would complete the hand. Regardless, the amount of tiles waited on is of course 9*4 - 13 = 23 tiles, same as Chuuren.
The 7gate is a tatsumaki extended with with a shuntsu on both sides, while the 8gate is an extended happoujibin.
Also, if 0 and 10 existed, Chuuren would wait on both, 8gate on the one next to the terminal, and 7gate on neither. So 11 gates, 10 gates and 9 gates? Arata would love the 2223456777789.