Let's say right now, everything on the Optima GT remains the same, CBU with RM 180k pricing. However, the car is now known as Toyota Camry GT.

Would you buy? 

As an Optima owner for 10 years (pre-K5) let me give you an idea. I exclude tyres as they are consumable items which depends on how much you travel.

Average per year over 10 years: RM2400
Excluding first 3 years as not typical, average from 4th to 10th year: RM2950
Average mileage per year: 22,000 km

I don't think the GT will be different by a lot. Bear in mind that my Optima was using timing belt which required changing every 60,000 km. The new Optima should use timing chain which doesn't need replacement.

Yes, I agree it could be lower. Main items were batteries, timing belts, A/C condenser (2x), engine mountings (2 sets) , lower arms, upper arms, ball joints, brake pads, absorbers, water hoses and radiator repair. I probably got cheated for the first set of engine mountings which lasted less than a year. The lower and upper arm and ball joints seem to give recurring problems so maybe I was given sub-standard parts as well. (There are also China made parts for Korean cars). This is the problem of using too many different mechanics just for convenience sake. In retrospect I should have found a good mechanic and stuck to him.

Maintaining a Korean D-segment is not much different from a Jap D-segment. My Accord averaged rm2000 a year over 8 years.

Be it mercs or BMW after two years!