D3 should really give you a free cover of your choice for your birthday, don’t you think?
yes. mine is next week. where can I order my OML yellow? thanks.
If by “cover of your choice”, they could just save time and give an oml yellow.
Or for the bad players a cho black 
My 2/5/0 OML would definitely prefer a red.
My birthday was last week, but I’ll take a late present.
Actually it may be a bit game-breaking to give away a free 5*. But I would even take a free 3* (IF) or a free 4* (JG).
A birthday gift would be nice, but that’s one more piece of personal info for them to give. Probably better to use the existing daily reward system, but put in more and better milestones for special dates, and maybe even flag them as anniversary gifts.
A cover of your choice would be tough, though. You either need to code a UI just for an annual cover selection, or every gift would require manual intervention.
Wasn’t some schmuck claiming he got a free Howard cover for his birthday?