As of the topic, once I got Malacca to be the most valuable trade node in the world, the tooltip updated to reflect Malacca and all is good, so it works as soon as you actually fulfill the criteria!
Playing as Ming? If you can't beat them join them, i guess

(sorry, still a bit salty about my last japan game where i had to fend them off in about 4 wars before i managed to actually beat them)
Is it fun? I've been thinking about trying it but i've heard the empire of china mechanics are too difficult for blobby nations. Basically if you border a strong nation you have to consume them... What's your experience?
I'm enjoying it, although I had a slow start due to some bad decision making that almost blew me up, so quite some time dealing with rebels.
My main goal is getting all the possible Institution spawns.
It's quite different with Ming as in I don't really do any diplomacy at all other than establishing tributaries.
As for the consuming neighbouring big nations: pretty much to keep the Mandate in shape. Once for me I was neighbouring a large Bengal allied with a large Delhi and it would have been difficult to take them on as I had my army very spread and was more focusing on getting more trade into Malacca, so I opted to release a vassal, so I wasn't neighbouring them anymore and got the Mandate growth up again. That way I was able to focus nations in nodes that would feed into Malacca.
I love the confucian religion mechanics, although they turned out a little too simple and powerful I find.
Idea wise, I grabbed humanism, exploration, expansion and trade, helping me to get those trade and new world institutions and deal with all the internal stuff. So far turned out really well.
The purpose of this play through for me was learning more about institutions, also increasing my trade game knowledge and exploring all the Mandate of Heaven stuff. Fun play-through so far, good for strengthening your weaknesses while still playing on Ironman.
Cheers!