Interesting, I'll try and cover some of the above from what I know.
Quad lift isn't new technology, it's in use in the far east in a few ports already, however they all differ from LGW in that they use a trailer to park system, LGW doesn't, it uses straddles, unless I'm mistaken these are only one box wide? They have obviously thought about the system but as yet I cannot see how they can land to quay or load from quay with a land side system designed around one box width, in the far east they use tandem width trailers to accommodate quad lifts. Typically quad lift frames have an interconnecting system that can move the boxes apart, usually only just enough to match cell guides or peg positions on lids, it'd be some frame that can spread far enough to allow a straddles wheels to pass between the boxes.
Regarding weights and safety systems, it is unlikely there will be any crane failures due to quad lifts and if used for loaded containers then special efforts will need to be made to ensure a balanced load. The problem with quad or twin lift is load balance, it is critical tat you do not load one wire more than the others (cranes typically use a four wire system), on current systems there is a percentage difference allowed between left and right wires and fore and aft or any single wire over the other three, typically 25%. If you try and twin lift two 20' and the difference between boxes exceeds 25% left and right then the crane will stop, by the same virtue if you have a load that has shifted in a 40' and is corner heavy then it will also stop.
Now if you quad lift then you will have an expanded footprint, whilst your left and right extremities remain the same your fore and aft are increased, leading to greater risk of a load differential fore and aft.
One other factor with quad lifts are box heights, the system will cope with height differences of 6" easily and some with great care will cope with 12", above that then it will not work. Imagine loading two 40', one at 8'6" the other at 9'6", the higher to seaside, that's fine but the next layer either has to be two identical boxes or a reverse of the above heights or else the frame will not cope.
Whilst your loading it's simple to make sure all your boxes arriving at the quay face are height and weight matched, but for discharge your relying on other ports to make sure box heights ans weights fall into your criteria....good luck on that one.
One other aspect, what happens to a crane when a vessel does arrive with boxes of varying height to discharge and load where quad picking is not an option, looking at the LGW press it shows a massive head block that is more than one frame wide, thus they cannot change the crane to a simple single frame option, that crane looks dedicated to quad lifts so will be parked up for the duration of the vessel.
It will be interesting to see how they get on, but I don't think it'll be a technology that many other European ports will rush to emulate, automated stacks, yes, but quad lift is a brave operation to run.
Regarding LGW recent poor box rate, it's they automated stackers they are having issues with, they can get the boxes off and on the vessel quick enough but are swamping the yard, the yard cranes are so busy trying to keep up with the quay that they then cannot cope with hauliers. All the recent three vessels they picked up from Felixstowe were poorly turned around, so much so that one left early after only discharging 800 of the projected 2000 boxes. Indeed Maersk then canceled the Maersk Kiel call, re planned the European calls so that it could call at Felixstowe instead.
Rumor on the quay is that Maersk only sent the Gudrun Maersk down there to see if such a large ship could transit in and out of there, which it could. It'd be wise not to discount LGW, they will get there once they have got over these initial teething problems and a recent shipping report shows that UK box growth has outstripped Europe and by end of 2015 we will be short of deep water berths in the UK, and that report already takes into account a finished LGW and berths 10/11 at FSR. If Ports can weather out the next 24 months then the indications are that there will be enough big boats for everyone.
Sorry for the extended dialogue.