Given that Phuket has become a high-end destination for the wealthy, it only makes sense that the main business area in the biggest beach town there will, in time, transition to catering to the trade of the wealthy, which will price out the mongers and most of us BMs.
But, the one factor that makes this seem less than certain, and which may account for why it hasn't happened already, is the nature of the land and its' owners in Phuket. Their considerable wealth is built upon the land, and at the core of their economic philosophy is the permanence of the land. When you own the land, then the wealth is forever, and cannot be taken from you. If you sell the land, then investments, stocks, bonds, etc., rise and fall. What seems golden one day, crumbles the next. I cannot see them being foolish enough to sell the land that has made their fortune.
Of course, in many parts of the world, where that same philosphy is adhered to, you have the 99 year lease. To get a major investor or corporation, such as Marriott, to invest the sort of capital that is required to build a first rate, high class hotel, they have to have, at least, a 99 year control of the property.
In LOS(correct me if I'm mistaken), the max lease is 30 years. I know that land is sold on the basis of 30 year leases, with two 30 yr options, for a total of 90 years(good enough), but, I have also heard it said that no one really knows whether those options are enforceable in a court of law, since the effect of them is to nullify the intent of the 30 yr limit on leases.
So, unless a major hotel operator can tie up the land, definitely, no ifs, buts, or ands, for 90 years, I don't see them paying the kind of money it would take to develop that property for high-end hotels. And I can't see the land owners selling, or even agreeing to options that would restrict their ability to charge as much as they wanted for the additional 30 yr leases.
This seems to me at the heart of why the sois are what they are, and why they may remain that way for the foreseeable future.