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)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.