Mario Kart 7 has the 1.1 cart which includes the update so you don't need to grab it from the eShop. Both the USA and EUR copies have been dumped.
When I updated my system (real NAND, on my non-Gateway system) and open up the eShop, it said something like "system has been updated, restarting app", and when it reloaded, I see this.
"The following changes will take place as part of the ID-linking process. Please scroll through and read this carefully.
Credit-Card-Information Management
Any credit-card information saved to this system will be deleted. In its place, credit-card information saved to your ID will be used, if available. Moving forward, credit-card information will be managed by your ID.
Account-Activity Management
Upon linking an ID, your Nintendo eShop account activity will be transferred to that ID. Please note that any account activity that predates this ID link will only be viewable within Nintendo eShop on this system--it can't be viewed on other devices. Please also note that after the link you'll no longer be able to delete your account activity from within Nintendo eShop. If you want to delete your account activity after the link, you'll need to delete your ID via System Settings."