Will Hong Kong motorists drive on the right side of the roads just like those in mainland China or the United States? I mean in the near future!

Currently some cars do have dual driver's licenses. A decade ago, Citybus drove its double decker buses well into Shenzhen from Hong Kong.

What a stupid idea.

Why should they change - it's not like the border is going to be removed. The cost to change the infrastructure is prohibitive even if it can be achieved - what is the point?
I rather them stay LHD like here, I hate driving in the US and other RHD countries.

Well, that's probably because you're used to the LHD layout. I'm used to the RHD but it would cost HK dearly to rebuild all the roads to reverse the layout. Because of the density of development, highways cannot be easily reconfigured as they are often very close to buildings.