Finally caved and purchased the 950XL from a Microsoft brick & mortar store. The sales associate told me I have to go through the Lumia Offers apps to get the dock, even though they had PLENTY of docks at the location. I said fine, I'll jump through their hoops.
Started up the phone, went through initialization process. Lumia Offers apps came with it. Loaded it up, no dock offer at all. Not even the recent promo Office 365 Personal FREE*. Updated all apps. Checked Lumia Offers again. Office 365 Personal FREE* popped up. But no dock.
Soft reset several times. No dock. WTF!!?? Performed hard reset. Again Lumia Offers was preinstalled. No dock offers. UGH!!!! Ran through updates again. Checked for the dock offer. No go! Office365 free still popped up. Could not get a second promo key for free Office365 though. Will update as I keep trying.
EDIT: Updated to .29. Checked Lumia Offers. Still no dock. After a minute, the 950XL stated it needed to reboot since there was a change to the SIM. Rebooted unit (aka soft reset). Checked again. No dock offers. Uninstalled Lumia Offers and reinstalled and soft reset several more times. No luck.
EDIT2: I was afraid the offer may no longer be available. I've done several hard resets with no luck. It just does not show up in Lumia Offers. I'm not sure if any new 950 owners have checked it recently, but it may no longer be available. Reading through the forums, others see the promo and click on it, and then it says it's no longer available or out of stock or whatever. But for me, it does not even show up at all. Chatted with MS help. They could not help me. Finally called MS Store phone number (1 877 696 7786). Spoke to them and they transferred me to another support Agent. After ~30 minutes of verifying my purchase and personal info, they were able to manually email me a link and promo code. Clicked the link and redeemed the code. YAAAYYY!!!
TL,DR: If you do not see the Display Dock in Lumia Offers app, try calling the main MS Store hotline (1 877 696 7786). They will want to verify you with either an email or text message. It's quicker with text message. GL friends!