etherize

Yes!  It helped me.   I was having some of the same problems you and the OP mentioned.  Followed your steps, and voilà!  It's all back to normal.  I've never installed a firmware update before just because I was afraid I'd screw something up.  Thought I'd read all the instructions carefully enough to avoid problems, but no.  Fortunately, I found this forum.

Unfortunately I learned my lesson the hard way when I pre-ordered the Nikon D800 back in 2012.  What a freakin' mess that was.  Now, my D800e is freakin' awesome. Anyway, I will not pre-order.  As a matter of fact, I think I'm going to kick back and wait until next spring or summer before I pull the trigger.  Why?  Because the reviewers online have their "rose-colored glasses" on and/or are using not only pre-production models, but are provided by Fuji.  What's the old saying:  Don't bite the hand that feeds you?  Or how about don't let the fox guard the hen house?  
 
In addition I have not seen a SINGLE review(er) yet discuss the image quality!!!  Have you?  No.  They are under orders not to until the camera is released.  Why would you or anyone order a new camera, basically sight unseen, which is basically unproven? 
 
Like I said, I won't make that mistake again.  I'll wait until all the pioneers take all the arrows, then I'll just come along and get the best of the best.  I'm in no hurry.  If I want added resolution from my X-T1 all I have to do is take a two/three shot vertical pano and wind up with MORE resolution than the 24MP cranks out anyway.  But I digress.  Yes, I will probably be buying one, but not until all the kinks (if any) are worked out, and not until the price drops a bit.  That's my story, and I'm sticking to it 

I'm remodeling a house so I didn't order the camera from B&H until TWO DAYS after it was posted.  I felt like the world was passing me by.  I blame the plumbers.

Edit:
Apparently I fail at reading comprehension. On the firmware update page for X-E2 it says for upgrades from 1.00 to 4.00 to execute SET-UP > RESET > SHOOTING MENU RESET and SET-UP RESET. After doing that everything works and I am back in business. Hope this can help someone else.
 
Original post:
I just upgraded to 4.00 from today on my X-E2 and have a similar issue. @perspektive says it worked fine for ~100 shots, but mine failed right away. I also Googled solutions saying to upgrade the firmware again, use different cards, reformat the cards before and after the upgrade, and different batteries, but also no luck.
  The first time I turn on the camera after the firmware upgrade: 1. The display only appears in the EVF, which is weird since I had set it to display in the LCD. 2. Taking a photo results in the rear LED to blink orange and green indefinitely 3. The UI is completely unresponsive at this point. I can no longer take new photos, change settings, go into menu, or interact in any way with the camera since I believe it's waiting for a disk write. 4. The on/off switch is also unresponsive. No way to turn off the camera except for ejecting the battery :-(   Any subsequent attempts to use the camera slightly differs in step 2: 1. The display only appears in the EVF, regardless of if I changed it in the last run. 2. Taking a photo no longer causes the rear LED to blink or to turn on at all. 3. UI is unresponsive again. 4. On/off switch also unresponsive. Eject battery :-(   This is definitely reproducible across my Transcend and SanDisk Extreme Pro SD cards, and my Fuji and third-party batteries.