That's how my Wii U bricked. I had already applied that huge update, bought, downloaded, and installed Mario, played Nintendo Land for a few hours, played a level of Mario, went back to the eshop to download ZombiU and Trine 2, then went to the download manager to watch the progress of those downloads.
Hard lock on the Download Manager loading screen. Unplugged the power. Waited. Plugged it back in. Brick. Red light of death.
Damn. I'm sorry that happened to you. Of course the warranty covers it, but it still sucks. I really really hope they fix this SOON. I don't want this happening to me or anyone else. Just know that your situation will help force Nintendo to address it so it doesn't happen again.
Oh, no worries. Nintendo is taking care of it, they were very gracious and apologetic, and my customer service experience was probably the best I've ever had, definitely far better than my experiences dealing with Microsoft, HP, Cisco, my internet provider, Amazon, etc.. I never got transferred or "escalated," was never on hold for more than a 2 minutes, I was obviously speaking with someone who was in my country (US), most likely up in Redmond WA. Just when you call the NOA help line, you can speak to an actual human being in less than 2 minutes, with just 3 button presses. It's pretty amazing.
And hey, I got to try Nintendo Land, which is mind-blowing IMHO, and I wasn't as much hung up on not being able to play on launch day as much as having the console to play during the winter break from school, when I don't have to wake up at 5AM every morning to get breakfast ready and pack my kid's lunch.
And while I know that my experience has been mirrored by many other people, it seems that the vast majority of people who bought on launch day have had smooth experiences.