Yes please: require 2 DT1-inclusions to reach DT2 (to avoid self-scratching).
2 DT1-inclusions wouldn't change anything much
I did the numbers a while back:
I counted DT2-inclusions on
Trust settings: there are 33 users with 0 (net) inclusions on DT2, and 308 with 1 inclusion.
But I don't think it's going to happen: although I believe this would be good for DT2, it doesn't really work with custom Trust lists: if you add someone to your Trust list, you want their feedback to show up to you, and that doesn't work if they'd need another inclusion from someone else.