This is an excellent Idea
and it would not take away from the 5 round title fights. This is also used extremely well in the K-1 fights.
But in order to make this happen, judges can not be afraid of giving out 10:10 rounds!
This should really happen! At least for a non title Co and Main Event.
It would also bring so much more excitement to the Sport. Just look how many fights go to the fourth and final round in a K-1 bout. It's just neccessary in such a combat sport!
Plus you said it, the entire immediate rematch thing would be gone.
Thats how it should be..
If there is a draw after three rounds, the judges' scores are thrown out and one or two extra three-minute rounds are contested. The judges' decision will then come from the scoring of each extra round only. If, after the extra round(s), there is still a draw, the judges will decide a winner based on the flow of the entire match, considering even the slightest difference. A fight can only end in a draw if both fighters go down at the same time and cannot get up, or in the case of accidental injury in the late stages of the contest.