I give them 10 years tops before violence. China may very well intervene if the Chinese heritage citizens are harrassed as they have been in the past.
Ethnic Malaysians, almost all of whom are Muslim, are about 55-60% of the population. As a whole, they are less affluent and educated than the Chinese and Indians who first migrated to Malaysia in the 19th century in order to work on the rubber plantations and in the tin mines. The predominately Chinese city of Singapore used to be part of Malaysia but was given her independence because otherwise ethnic Malaysians would be a minority in their own homeland. The Chinese and Indians, along with foreign investment (I used to own a GE phone and answering machine made in Malaysia) are largely responsible for the relative prosperity of Malaysia.
If the Muslim radicals continue to make trouble, I assume that the foreign companies may simply choose to relocate to China (most of the factory managers are ethnic Chinese), Thailand or Vietnam. To be fair, I suspect that many Muslim Malaysians are unhappy about the Saudization of their culture; for example, Muslim women by law must now cover their heads, arms and legs in public. Funny in a way -- imagine a Muslim woman, wearing a head veil and a full-length, loose-fitting dress with long sleeves walking by a Chinese girl wearing a miniskirt and tight tank top! Eventually, the Saudi wannabees may begin to pressure the large non-Muslim to dress more in accordance with Wahhabi norms.
You made an interesting point about China intervening on behalf of a persecuted ethnic Chinese minority. Malaysia would certainly be be a nice prize, with her mineral wealth and strategic position on the Strait of Malacca. I wonder about India intervening on behalf of a persecuted Indian minority. India has her own problems with Muslims.