If that was the case, other cars should face the same problem too 

In the past, NAZA did not manufacture KIA car here. So most (if not all) spare parts came imported from its country origin in which i have to agree that spare parts availability & cost is in jeopardy.

Since that NAZA CKDed the Forte here in Malaysia, i believe that most of the spare parts should be easily available here in years to come 

I believe K3 Cerato still will have some parts same as current Forte. This happened everywhere. The Samsung LCD/LED overtook Panasonic / National TV 7 or 8 years ago, the Samsung, HTC, iPhone mobile phone overtook the Nokia, Sony Erricson as well.
Therefore doesn't mean today you own something big in quantity you will not have problem in next 5-10 yrs down the road.

The Forte still have 5 yrs warranty. Do you think KIA stupid enough to create spare parts totally new for K3 Cerato? All spare parts will be share share use by different model. This is nature of business.

shouldn't be same unless they have shared parts which is doubtful..two different generation of cars..

Isn't it too late to worry now?