Well, Shang Villa in Kelana Jaya managed to convert to freehold for some odd reason.

http://www.propwall.my/kelana_jaya/shang_villa

I still don think its possible under normal circumstances else all the JMBs will ask for freehold conversion dy ~
something is under the table ~ LOL

you are semi correct.
however the conversion is on value of land as conversion involves the land only and not the building. hence one should deduce the land value and not the property value as base for the application for conversion.
and again you are right to say for highrise, you would practically require almost entire agreement in place (>90%) in order to proceed with application.
say 50% owner willing to fork out the additional for conversion, the other 50% or even 10% might not and it still would not go through.

thank you for your kindly reply...actually i'm planning to buy a house with leasehold status...the location is perfect and the price is good. but it only got 50 years left....after read all the reply i'm not sure whether it's a wise decision to buy this kind of house...