You're SURE it (PH) will go well in 5 years.... and "sg market could tank spectacularly, along with HK and Aus.... Global house price bubble popping is not an outside bet but a real possibility."
Your statements and guesses are all running wild! We can imagine a lot. Anyone can make predictions with no one being a God to confirm their certainty.
Based on facts and data alone, I'd say it's more likely for properties in Iskandar region within the next 5 years, be it Medini, PH or elsewhere, we should see price stagnation (or even reduction) for some time due to the huge oversupply coming up. How they will move after that is anybody's guess. But I think this is more likely to happen.
Despite the fall in RM and developers dangling carrots for their properties in Iskandar, the sales have been extremely slow. Investors and general buyers are wary. But for SG, the govt is holding tightly to the cooling measures with no end in sight. They know the moment they release some of their grip, there will be tons of people rushing in to buy. As it is, even with those measures, recent sales have been robust. This speaks a lot about the different sentiments at both sides, SG and Iskandar.