Looking at the posted article and videos, it looks like there's an easy connector built in to the luggage block, rather than a cable which you manually unplug. This is great for taking the pack off quickly and easily, but as I mentioned above, not great if you normally use the luggage block for luggage.
I can only imagine that Brompton will develop (or have developed) a bigger combo bag that houses the connector and battery pack plus leaves room for you stuff.
It's pretty short-sighted if not.
As for my earlier comment about not being able to fit SPDs, it looks like the sensor is housed in the bottom bracket - hence the need for a larger shell - so you'd be able to fit whatever you wanted.
Standard bike comes with a 1.5L bag containing the bike. There is also an option for a larger bag which I assume is also designed to take the battery (with space for luggage)