I like the idea of Australia if they're not experienced travelers. It's multicultural and welcoming, English is spoken, and it will seem different and exotic to them. It's also a very easy and efficient place for visitors, clean, safe, etc. There are beach resorts but also fascinating cities. If they have time, Alice Springs/Ayer's Rock/Darwin/the Outback would be very different, but something like Great Barrier Reef, Sydney, and Melbourne would be a very nice first taste. A stop in Perth would break the journey, for instance if they route through SIN, which would also be a good stop to add for them (and still easier than Hong Kong).