What if Iskandar Muda ('the young Alexander'), sultan of Aceh, had successfully emulated his namesake by crushing a once-mighty empire? That is, what if Aceh had successfully captured Portuguese Malacca in 1629?
This is incorrect. Johor was very weak at this point, having been shattered by seven Acehnese invasions. Iskandar Muda sacked its capital as recently as 1623. Johor actually supported the Portuguese in the Acehnese siege of Melaka because it correctly perceived Aceh as a far, far more powerful threat.Johor would become Aceh's greatest rival.
As long as the Dutch don't screw with things, I actually think Aceh could control the Straits indefinitely. Once it has ousted the Portuguese and destroyed Johor, there's nobody left who can contest Aceh's claim to be the center of the Malay world and rightful heir of Malacca - that is, there's no ideology that Malays can use against Acehnese control. The Dutch are the only real problem for the 17th century (other Europeans are still rather weak) but Aceh isn't a direct threat to VOC interests.although I don't think Aceh could keep said Straits for any lengthy (as in, like, a century) period of time.