I'll tell you a secret. I deserve a tiny bit of the blame for the SP delegation feature. Back in 2016, a few of us started Project Curie. There were whales who would support by trailing our votes. Since there was no delegation feature, we worked out a deal where a script would track how much rewards Curie's votes were generating for their account, and they'll donate some or all of it. The SP delegation feature was designed as a response to make this easier. (It also had other drivers, such as making account creation with delegation possible, of course.)
Anyway, while I agree with your idea, ultimately that's simply what will happen if there was a delegation fee - people will go back to how it was before the feature existed. They would just follow the voting trail normally, and have a script do the calculations for the rewards generated etc.
very interesting and thx for the feedback, simulating delegation with a script and sharing rewards sounds interesting but also a bit complicated and perhaps would stop some users from using bid bots and just curate themselves. Because Steemit is a very complex and dynamic system, I think we should try out some promising proposals, test them for a predefined time (for example a week or one month), and if the results are good, keep the change or otherwise roll back the change.