I would tend to agree with this idea.

My wife has an ice-cube's chance of ever breaking into Gold territory with her infrequent flying, so LP's she earns are essentially useless. Steering her LP's my way (since they were paid with my wallet) would be nice.
I would then contend that LP's earned by her CC should also flow to my account - which is something we could accomplish via an Authorized User on one of my cards.
But I think OP's idea has close to zero chance of materializing into actual AA policy.

All that said, I usually burn AA miles for my wife's tickets and pay cash for mine.
Since we have plenty of RDM, and her tickets are really just leisure travel, AND we have no interest in her earning status.
Don't want to give AA actual $$ for her tickets, since the marginal gains of a cash ticket over award ticket don't have much value for her.

Just my 2 cents on OP's idea.