Oh, thought it was standard equipment for the last 8 or 9 years
Like most things with Boeing, it's a latent capability, but you have to pay for the capability and the FCOM supplement. It does seem daft that they provide all these capabilities in the software, but their commercial department puts all these false price differentials in, similar to the different levels of detail available in the FCOM for different amounts of cash.
VNAV PTH in approach does have one or two oddities that one may not encounter in normal ops, and has confused me in the sim before - if more than 200ft below the path, it will command a VS of 0fpm until back on the path.