I see no reason for a 10% cap on delegate transaction fee cut. Why shouldn't delegates individually allocate 100% of transaction fees between destruction for dividends, their own cut, and funding development or charity or whatever they think the stakeholders want?
The inactivity fee could just be replaced with total destruction of funds after a year or so of inactivity, but that might make people nervous. Is the another reason for the inactivity fee besides eliminating the need for permanent storage of old blocks?