To summarise from the skytrain section..
The MRT system is missing stations at NE2, Woodleigh, and NS6. Of these, Woodleigh is partially? constructed, while there are no signs of provision for stations at NE2 or NS6. Buangkok has been completed but awaiting opening while SBS accountants count their pennies. NE6, Dhoby Ghaut, definitely exists
There's also a station missing between NS11 (Sembawang) and NS 13 (Yishun). This area is under development with new HDB blocks going up, and a new station will be more feasible here than between Yew Tee and Kranji which is currently an industrial area with scungy dogs roaming around. Last time I went by, Canberra Link, the road running parallel to the MRT between Yishun and Sembawang, was being put across the canal.