Can you add another option? We certainly plan to stay for a good 5 - 10 years plus, as our quality of life here is significantly better than it would be in London - due to tax, earning potential, cost of commuting and everything other than rent.
But I wouldn't say we'd stay forever - HK wouldn't be somewhere we'd choose to retire or downscale for example, as the cost of living is high and the pace frenetic.