The iOS 12 beta which was released a few days ago consisted of configuration setups similar to those in dual SIM devices.
Per Tech Crunch:
There have been rumours in the past that Apple was looking at selling iPhones with two SIM cards. It was unclear if Apple wanted to put a normal SIM tray and a second e-SIM card like on the Apple Watch.
But according to these configuration files, this model will let you add two physical SIM cards — there are references to “second SIM status” and “second SIM tray status”.
A dual SIM feature is an essential feature for regular travellers who can buy local SIMs to avoid expensive roaming charges. It is also very useful for the users in India where the cell carriers are regional companies.
h/t: Tech Crunch