There seems to be so many differing opinions on the conservation rules.
Taking a simplistic view, the only thing which cannot be touched is the conserved facade for EMG i.e. the front mandarin like tower fronting the drive-in. If the entire site was conserved, the developer would not have been able to tear down and build the current 10-storey structures in the first place.
A case in point is the butterfly house along amber road (the devpt is called Aristo). Only the driveway and part of the lobby are conserved, the rest of the building is built up to the max permissible height.
For any URA rules, as long as it is not explicitly stated, it means that developers can always try their luck. Whether URA approves or not is another matter.
For the GPR calculation, assuming the site area is 108,000sf, the max permissible built up is 3.5x108,000 = 378,000. This however, is the GROSS built-up which includes all common facilities etc. Usually, condos have an efficiency of around 80% i.e. actual saleable area is around 80% of gross built up. Assuming an 80% efficiency, the max saleable area is 80% x 378,000 = 302,400sf. Assuming 'Guest' guesstimates (pardon the pun) are right about total strata unit areas of 289,000sf, there is a small buffer of 13,400sf which has not been utilized. There are many blocks in EMG at the current moment. A smart developer could always build a single tower block with numerous studio units to capitalise on the heigt potential of the PR. Go figure how many studios of say 500sf can be built with the current saleable area.The surrounding areas can then be extensively landscaped with tennis courts, lap pools, saunas and jacuzzis, reflection areas and the whole devpt marketed as an 'Oasis within the CBD'
The story becomes more attractive of course if the increase in PR becomes reality which stands a very good chance given the MRT proximity and misc other factors which I cannot reveal. Always trust Baby (have you ever known babies to lie ???)
All in all, regardless of whether there is an en-bloc potential, the devpt itself is a very nice and quaint condo which is easily rentable. I always have good vibes when I visit the place. If you consider all other alternatives, the availability of FH or 999yr sites right smack in CBD/Marina bay area is severely limited.