Using the Broadcom AFBR-S50 with Arduino
I recently looked into this again, and it turns out that Broadcom had released a porting guide for this library in August 2020 (nearly a year after I originally posted this question) that should prove useful to anyone trying to make use of this sensor. It's for the STM32 platform, not Arduino, but it's the most detail Broadcom has provided with regards to this product, and should provide a starting point at least.
I happen to have access to the Nucleo board used in the guide, but I had some issues with following it in some cases due to some differences in the SDK file/directory structure. I did eventually get a passing build out of it, but couldn't get anything out of the sensor itself, which means that I either did something wrong, or had damaged the sensor in my earlier attempts to interface with it; at the time of my last attempt, I was leaning towards the latter. I don't think I'll be revisiting this unit any time soon, so hopefully others will have better luck. And if anyone does get it working, please do report back; I'm curious to know if I'd actually be able to use this thing if I were to buy another one.
P.S: I'm not marking this as answered because a) my question was technically for the Arduino, and b) I haven't been able to confirm that this is working.