Create separate group for i2c buses in /dev
I suggest to create new group (i.e. i2c) and make i2c bus devices belong to that group with udev rule like
KERNEL=="i2c-[0-9]*", GROUP="i2c", MODE="0660"
There are tools like ddcutil (change monitor settings via command line) which requires access to i2c buses, but are useful in everyday activitiy of a non-root users.
(from redmine: issue id 9015, created on 2018-06-15)