The only remaining expansion space at LCY is to the east of the terminal. A straightforward pier out of the terminal on that side, set further back from the runway allowing more manoeuvring space than the present stands (which were sized for Dash Sevens and are a squish even for 146s) would be the most effective.
Key problem is it is over the dock and therefore requires an expensive civil engineering job to fill this in, hard up against the terminal, although the bulk fill material could be brought in from the river by barge.
Anyone who has been there recently will know the mess that the DLR extension has created (and for something called "light rail" the viaducts appear to be sized for TGV trains !). Before long they may need to put a multi-storey structure onto the car park as well (which means you need space for a year or so for a temporary car park - the space for the terminal extension could be needed for this first). So potential building works for years to come.