Increasing ESP32 AP max connections
After some extensive testing with several modules (not just blindly trusting the documentation), here's what I found.

Short answer : maximum 10 AP connections for the ESP32 running ESP-IDF 4.0 (updated around 1st of march 2020), and no, it can't be increased (easily).

Details :


The maximum number of AP connections is defined somewhere in libnet80211, and can't be modified since I have no access to the source code.
when the 11th station tries to connect, libnet80211 prints I (39682043) wifi: max connection, deauth!, more or less like the ESP8266 for the 5th station
Changine the ESP_WIFI_MAX_CONN_NUM (defined in esp_wifi_types.h:258) from 10 to anything else ends up in unpredictable behavior (I'm labelling this as unpredictable since without the libnet80211 code, it can't be reliably assessed).


I'm not giving up on increasing the number of stations yet, so maybe there'll be an update to this answer.