I brought this up in #super-mario-64, and the minor consensus is that 100 Coins is "possible", the same way Red Coins is possible.
According to a FAQ online, DDD has 106 coins. That means you are still required to get at least 5 of the red coins in order to get the 100 coin star. If we already have a rule stating the Red Coins require the sub to be removed (by reaching Bowser in the Fire Sea), it should apply to the 100 coins as well.
The consensus on it being "possible" was that it requires a very specific triple jump. There is no "Strict" category for this since it isn't caps/cannons-based, but it is extremely unreasonable to casual play. If you want to sequence break it, go for it, but I don't think it should be expected.
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