I'm not so sure it isn't an idea worth looking at. There is a reason that the mother's educational level is regarded as the best indicator of future success, after all.
It's not, necessarily, just about homework support, as the OP acknowledges, but about everything. I've said this before on here - a parent that can negotiate paperwork and complex admin systems, can write formal letters well, can support and comprehend new systems of learning (phonics, anyone?), can talk on a level with a teacher without being intimidated, can expand a topic through their own interest in it, etc, etc, etc, obviously advantages their child over the parent who can't.
We saw that, in a thread the other week. The OP was barely literate - and, accordingly, having nightmares communicating the requirements and restrictions of a complex medical condition her son had to the school.
And economic success, now, isn't the best measure of that. How you would administer it, though.... Perhaps a combination of job role/educational attainment/hours worked?
I'm amused by those saying things like 'my parent only got this, but is a fully qualified whatever'.... er, in a lot of those cases, that would be a qualification granted at a college or a university, and therefore, raises the educational level from the basic!