As it coincides with the store and accounts system being down, presumably it's all related. I just hope it isn't to do with crown gifting, there must be better things to shut everyone out of the game for - for what is for some effectively the whole day.

Unusually, however, ZOS are implementing an extra long downtime without bothering to tell us why. That suggests to me that it's something they don't want to talk about.

Yes, an eleven hour scheduled maintenance is pretty unusual and rather challenging for the play schedules of many players. I'm surprised the devs are not sharing with us what is it about. An explanation goes a long way in garnering support/patience from the players I should think. And helps avoid the speculation that tends to spread in a vacuum.