From what I know, most "local" (these are actually international companies with overseas HQ's, but providing medical plans which are adapted to the local market. eg: AIA, Manulife, Prudential, etc.) insurance companies take a pre-existing condition as an exclusion.
If we are talking about the so-called "expat" insurance companies, they can underwrite new applicants on a 12- or 24-month moratorium (waiting period) in respect to any pre-exisiting condition. Also, most of these "expat" insurance companies will consider pre-existing medical conditions which has started to occur 24-months before the individuals application.
Even Bupa, which is loved by many expats, provides the following details on their website:
Q) Am I covered for pre-existing conditions?
A) We will not cover you for any illnesses you are currently suffering from or have had before. These are known as pre-existing conditions.
A pre-existing condition is any disease, illness or injury for which in the 7 years before your start date:
- You have received medication, advice or treatment; or
- You have experienced symptoms
Whether the condition was diagnosed or not.
If you have a pre-existing condition that may need treatment in the future, we will usually exclude it from the cover along with any conditions related to it.
Then my personal experience with the Public Healthcare system in Hong Kong:
What do you think about public outpatient clinics?
- It is for sure not bad, but because the public system tends to be understaffed it can be quite hectic and extremely busy in there..
Did you experience it?
- Yes. I had a bad cut on my finger with blood gushing out and went to the A&E at Queen Mary. The moment I stepped in they gave me an express pressure bandage and labelled me as semi-urgent on my waiting ticket.
Did you queue for it?
- Oh yes! 4 hours... I spend a very memorable Friday evening there 
What is your point of view regarding our situation?
- Can't your current healthcare provider offer international packages? Because you described them as "one of the best insurance coverage of the world". I know many EU national insurance companies provide international packages to their national clients' when they move abroad.
Also since you have about 2 months left you can try to contact the private hospitals in Hong Kong and enquire if they provide the specific medicine which is needed for your wife, the duration of the treatment and most importantly the costs.
Good luck!