Measures against Overdelegation
Couldn't we implement a "Tag" for tz1 Accounts; "Delegations accepted", like we have it already for KT1 Accounts with "Delegatable". This way a Delegation-Service could Tag its tz1 Account with that flag and every Delegation-Operation to that Account fails from that point on.
Like a "Shop closed" sign. This would empower the Delegation-Services, to have more control about the overdelegation.
The helpless " please stop delegate to us" can not be a permanent state. We have to give the Delegation-Services a tool.
Further thinking; Wallets could check, if a tz1 Account has the flag "Delegations accepted" to avoid Gas waste.