Few things I think we need for delegation:
A way to withdraw a node from public delegation. Ideally a flag on the contract (public delegation yes/no).
Ability to allow delegation from pre-defined authorised wallets (validator defines list of wallets that can delegate). So that validators can set non-pubic rates from business deals etc. (this would solve 1 - as a validator would define their own wallet as the only one that can delegate) Also, UI could search for any text in this field, and if so, no display these nodes in the public delegation UI
Ability to adjust lock in terms from the contract (again, for bespoke deals/arrangements - i.e. 2years lock in preferential fee rate)