Breadboard ends, any restrictions?

Hello all, I am about to start building a farm style table for some friends. Using white oak, top will be about 7'L x 42"W x 1-5/8" Thick. They would like breadboard ends, and they would prefer the breadboards to be 8-9" wide. Looking forward to the build, but I have always seen breadboards being about 3-4" wide.
Are there any practical/structural restrictions on breadboard widths, or any precautions I will need to deal with on this?
Also, I am used to the rule of thumb of the tenons' length being 2/3 the width of the breadboard. In this case what would you recommend?
Thanks much!
Tom G

Btw, I intend to attach the top to the aprons using metal z clips to account for wood movement

I would steer them away or explain the issues if they insist.

Personally I wouldn't do a breadboards over 5" wide. I use 2/3 as a depth.

Depth of tenon and support are issue on wide ones.

There is no reason why the bread boards can't be that wide or even wider as long as the table apron supports them. you still need to account for the seasonal dimension changes in both the center and the ends.

Thanks for the responses!
I do plan for the top to overhang the outside face of the legs by 3-4" on each end. So that would put the legs/apron pretty much in the middle of an 8" wide breadboard end. Does that seem to be adequate support to overcome the concern that Robert brings up?
Also, should the tenons still need to extend 2/3 of the way (5.25") into an 8" breadboard? Or can do with less than that?

I think tenons 2-3" long wold be adequate, be sure that they allow the main field of the table to expand and contract seasonally. the one in the center can be glued so that the bread board stays centered.

I think the weak link here is the mortise depth on a 1 5/8" board. Dividing the board in thirds leave a .54" tenon and 2 .54" tongues (for lack of a better word). Having the wide breadboards supported by the apron somewhat mitigates this. A 2"+ mortise depth is plenty strong in this case. My $.02 for what it's worth: 2 cents!