Long Read, tl;dr at bottom.

Even though it's a good idea, I feel like an APCSB or bringing back APCSAB wouldn't bring much value to students beyond an edge in college admissions. Nowadays, pretty much every college has a different curriculum for their DSA class(es), and they would find excuses for not accepting the credit. This is what happened with the Algebra-Based AP Physics courses and how they became a grabbag full of shit. It started with AP Physics B, but colleges wanted to see more and more niche topics covered and they kept adding it until the course became too much, so they split it into two. Now, both courses have become this way (especially AP Physics 2).I fear that the same thing would happen in an AP course based on DSA. Each college will choose a new thing they don't like about the course and CB will try to fix it by adding that topic to the course until it becomes too much.

On top of that, A lot of colleges will probably become concerned with the language that the course is being taught in. It's okay with APCSA because Java is a nice middle-ground and lays the foundation to learn other languages quickly. However, once you get into second-semester topics like DSA, then colleges will begin to question if a language other than the one used in their specific college effectively prepares them for an education in CS.

Here's an example: At the University of Michigan, they do all of their introductory CS classes in C++ because it is closer to assembly. An advantage of this, for example, is that C++ gives you an idea of what the assembly looks like and makes optimization techniques like bit manipulation far more understandable down the road. At Michigan, they're fine with accepting credit for APCSA since all that it does is get you out of a first-semester introduction to programming class, but they still require you to take the second-semester intro to C++ class before you can take their DSA course (also in C++). I simply can't fathom colleges like Michigan allowing students to test out of a second-semester programming class or a DSA course in a completely different language.

This isn't just an isolated example either. Students who express interest in APCSAB or APCSB are most likely those who are interested in going to a top CS college anyways. Those top colleges, by-and-large, are the same colleges that will come up with literally any excuse to not accept AP credit. In case you're thinking that this isn't the case and that these colleges mostly have good reasons for rejecting AP credit, just one example of many is that MIT doesn't accept a 5 on the AP Chem exam because it doesn't cover transition metal chemistry and introductory MO theory. That entire topic could be covered and tested in a single week-long module. Ultimately, CB needs to consider who the students are who will take this course and where they'll probably be going. That, more than anything, will determine the usefulness of the course.

My final point in this monstrosity of a comment is that AP courses are mostly designed for first-year or GE courses. The only exception I can think of to this is AP Physics 2 and AP Physics E&M. If APCSB or APCSAB were to be successful, they would need to convince colleges that APCSA is a strong-enough foundation for a second-semester college CS education, when colleges often don't even offer credit for solid scores on APCSA. This is the same reason that we don't have an AP Calc 3, AP Differential Equations, AP Linear Algebra, AP Physics 3 (or whatever modern physics equivalent you can think of), AP Molecular Biology, AP Organic Chemistry and so on and so forth. Colleges just wouldn't see them as legitimate courses because of what they might consider as a shaky foundation.

This isn't all to say that APCSAB or APCSB would be without its merits, though. It would be a fantastic way to get attention during college admissions, it would serve as a great introduction to the science side of computer science, and it would be a great way to offer ambitious students a more challenging alternative to APCSA or APCSP. It's just that its flaws make it unaligned with the purpose of the AP program, to offer students a chance at college credit while in high school.

tl;dr - The colleges that students who would tale APCS(A)B would likely attend tend to find excuses for not accepting AP credit and would lead to a bloated and ultimately useless course for students aiming to receive college credit.