Millions of guests attach their tickets to their accounts which show up on their MBs or MB+. My
MDE account on DL is the same stuff as MDE for WDW. Tickets attach the same way. They are already planning on attaching millions of guests for MB+, they don't think just a few thousand will buy MB+.
As far as attaching to a ticket when you purchase DLR tickets and put them on the app you assign them to a person the same as you do at WDW. When you get a MB you have to pair it to a person. I'm looking at these steps for MB+ (albeit for WDW because DLR isn't out yet) and they do not appear to be any different than MBs in pairing to a person. In order to pair to a person through the app you have to have a profile for them (even if you're all under one person who is managing their account). I agree it would be an added thing to one's profile but no more than what exists already with WDW MDE. What I guess I'm trying to convey here is we're not talking some earth shattering thing. The apps already function very similarly, the MDE profiles as well. I mean they make you have the same login info across all platforms lol.
I'll only address this because this is the crux of your confusion: the WDW and DLR systems are
significantly different and do not work the same way, even if they behave similarly in the apps.
WDW's system focuses on the
user. You buy a ticket, you attach it to a
user. You buy an MB, you attach it to a
user. At a WDW entrance gate, when you tap an MB, it looks up the user and checks to see if that user has valid admission.
Critical difference: DLR's system focuses* on the
ticket, not the user.
At DLR, you buy a ticket, you assign a name/user to it. When you buy a DLR MB+, you attach it to a
ticket, not a specific user. (That's spelled out in the announcement today.)
At a DLR entrance gate, tapping an MB will simply pull up the ticket attached to it and show the CM the photo attached to that ticket.
Even if the apps sorta resemble each other, that's a
huge difference in functionality and operations. And that's a substantial reason that bringing in MB2 will be more complicated than it seems.
Btw - the difference opens the door to some odd scenarios that DLR hasn't addressed yet. For example, what happens to an MB+ after a ticket expires or is fully used - can it be attached to another ticket? Can an MB+ be moved from one ticket to another?
WDW permanently locks MBs to a specific user, but there is no such thing as a "specific user" at DLR - just whoever's name (and photograph) is on the ticket or pass.
* There are parts of DLR's system that are tied to user accounts, such as dining.