Here’s the first problem in no particular order: lack of self-containment.
BBR is heavily linked to other projects I had in mind. Those included the tie-ins in the same universe (such as prequels) and some other stories that barely had anything in common with BBR aside from some deus ex characters (such as the Seven Deaths). At this point, I can’t even begin to take all the references away without very, VERY major rewriting of the plot.
Now, there’s probably nothing wrong with the stories being linked with each other. In fact, I often enjoy those if they’re done right. So let’s talk about this idea for a sec.
I don’t read that many superhero comics, but I do know how many characters and stories are intertwined there. So if I pick up a comic issue with a superhero I know and love, and they randomly team up with a superhero from another comic series I’ve barely ever heard of, my experience will be either:
A) It doesn’t affect the plot and the storyline is crystal clear to me, despite my ignorance of the foreign series. There may be some confusion about the other superhero, but it’s minor and doesn’t ruin the understanding of the situation. If I’m still curious about, I can research some stuff on my own, but it’s not mandatory.
B) It affects the storyline to the point of me being greatly confused. I HAVE to do some research of that other superhero to fully enjoy my fav series. What if I’m not interested in it? Well, sucks to be me!
The knowledge of your other works shouldn’t be required from the reader.
1. Don’t expect them to drop everything and start doing their homework to even begin to understand your plot. They’re probably going to drop your comic instead.
2. What if those “other works” don’t even exist yet? What if you’re never gonna make them? Without those tie-ins even your magnus opus would make no sense.
3. Comic publishers often do this kinda thing to sell you another comic you wouldn’t be interested in otherwise. That’s cheap and unpleasant, so don’t do it just for the sake of that.
On the other hand, hint-dropping and characters making cameos can be just fine. In fact, it’s great because later you can always point on those hints and say “See? It’s not an asspull!”. I love these kind of smart details! Again, it depends on how subtle you’re being with it and how much it affects the plot.
BBR was as subtle with it as an elephant in a porcelain shop.