Well, there might be small antennae, but there is a limit of how small can still receive a usable signal, especially if it can not be placed ideally. But looking at the size of modern integrated GNSS receivers there is no doubt they can easily be placed anywhere on a new board. See here the Broadcom chip
https://www.myfixguide.com/wp-content/uploads/2017/06/Huawei-Honor-9-Teardown-25.jpg
As far as I'm aware there are now combined antennae for WIFI and GNSS, maybe also BT. I would not exclude that therefore a breakthrough at the prism housing might just not be necessary anymore. Still, for GPS and Beidou, Glonass, Galileo... this antenna should be in an upwards facing place. On the other hand the right side grip (with the obvious breakthrough in the metal shell) would be a part that would (for traditionally trained photographers) be placed on the upper side also in portrait orientation.
See here the combined BT and GPS flex antenna for iPhone 10 X
https://www.ebay.de/itm/iPhone-X-10-Bluetooth-GPS-Signal-Antenne-Flex-Antenn...-/293300332598
Someone posted the spec sheet from a german page. They probably have their information also only from the official Ricoh bits we are aware here too. They do list "GPS", and, what I find interesting is that in the accessories they don't list an external GPS/GNSS module. But both could just come from copying missing fields in their spec sheet with data from e.g. the K-1.