Should we be teaching fact families with 8 facts?

Hi,  Did you ever have an idea you just had to throw out there and see what people think? 

I have been noticing that it is really hard for kids to complete equations such as: 

8 = 12 - ___.

To complete these equations, they really have to understand the equal sign. 

Then, I got to thinking ~ what do we usually teach them regarding fact families and/or related facts? 

Four basic facts, such as:

2 + 3 = 5

3 + 2 = 5

5 - 3 = 2

5 - 2 + 3

Is it time to introduce a new fact family? A family with 8 facts? Here's what I'm thinking: 

I'm thinking of creating a series of activities based on this idea and thought I'd ask what you think of it first.

I know I'd have to build in lots of support to get kids started. If you have a moment, I'd really love to hear your thoughts . . . . 

Many thanks for stopping by!  :) Anne Gardner