As of today, there isn't much of an advantage of doing a SiP for a chip like the AM335x other than the high speed design. Most of market is still with PCB SoMs for larger cortex-A chips.

The real advantage of SiP is with BLE or similar. That's because not only do they take away the complexity of RF design, and regulatory certification i.e FCC, IC, CE etc.. The market for BLE SiP modules that integrate the crystal, Balun, Antenna and are are certified is exploding.

Just a year ago, the cost difference between a BLE module and BLE chip was large enough to justify doing a custom design for anything more than 5K Units/Year. However, the Math is slowing moving towards higher and higher volumes. Already anything that ships less than 20K-30K per year doesn't justify the cost of doing a custom RF design.

Maybe in a couple of years, there will be a mass market for Beaglebone SiPs. Just not yet.