There's bound to be chaos at the beginning. But I'm hoping it'll work itself out - things often do. If it's really horrendus, people will carry on to canada water on the tube. The people that will want to keep using the Southern services the most are the ones that don't already use the underground. I'm not sure what % of passengers this is. Of course others will want to as well, but if it really is bad (i.e, can't get on the train bad) it won't take too long before people abandon it for the ELL.

But I wouldn't be surprised if it's dreadful in the first instance - especially if the 4 tph are cut down to 4 carriages.