Steem's supply is based on the Proof of Brain method of mining. Non-Brain Proof Mining causes counterfeit steem, in my opinion. Counterfeit causes inflation if not removed from the economy.
If one could delegate only one step and not be able to delegate delegations, it may put more Proof of Brain back in the mix.
Regardless if it is a good idea business-wise with perhaps having some ethical issues, a witness is a political beast as well as an admin. For that reason a successful one needs handle themselves differently than your average user.
P.S. These views are my own. This witness project is being run by another admin, as you would know @wiser, yet others may assume wrongly.
My understanding of delegation voting was mistaken. It seems that 'brokers' arrange an exchange. Pairs the delegators and delegatees only. Delegation can only be passed in that one step. So this is where Proof of Trust enters the picture. Never liked karma points yet they may have an unobserved purpose here. ;)