Motorola's MotoMods were the last reasonably successful attempt to make modular smartphones with hot-swappable features, and now it appears that Huawei plans to introduce something similar. However, while MotoMods communicate via pogo pin connectors, Huawei and Honor's accessories will use Bluetooth, as recent Bluetooth SIG certifications suggest.
https://www.notebookcheck.net/Huawei-develops-Bluetooth-smart-cases-Mate-30-with-modular-add-ons.434051.0.html