Like Vman455, I've been rolling with various exterior/interior mirror configurations for many years now (15?). Currently,
on my Mirage, I've replaced the outside mirrors with internal convex ones placed close to the glass.
Another potential disadvantage: while interior mirrors preserve much of the side view (some even expand it), you lose the ability to look directly down the
side of the car itself. That can make reversing into tight spaces a real challenge.
Also makes it harder to spot cyclists when pulling away from the curb in a line of cars, if the cyclist is riding close to the cars.
You would of course adapt for safety's sake (eg. with exaggerated shoulder-checks, or cracking open the door when reversing in close quarters).
But I'm planning to modify my outside mirror blanks to add exterior mirror "slivers" - mostly to aid reversing into tight spots (by tight I mean just inches to spare from the side of the car).
Retractable/pop-out mirrors would also be fun... and more aerodynamic.