Sharp and CDT is probably my #1 preference.
I'm in danger of sounding like a broken record but our ruck stocks are essentially this:
Nank (workhorse + gets banged up)
Ryan (crap)
OHB (crap + likely to never debut)
Sims (kid + forward/ruck hybrid)
CDT is more of a ruck/forward hybrid and in 5+ years I think him tag-teaming the ruck/forward duties with Sims would be a great plan, with Armstrong and Faull the two permanent tall forwards.
Would be happy with duursma over sharp as well.
If you look at the projected future side - something like.
Miller. Gibcus. Balta.
Brown. Trainor. Banks.
Rioli. Smillie. Mansell.
Algar. Faull. Lalor.
Campbell. Armstrong. Taranto.
Sims. Hotton. McAuliffe
The wings looks close to the greatest area of weakness. Duursma would instantly improve that.
Other options like trezsie and co. Are suboptimal too. .
CDT is a risk but you don't often get the chance to take unicorns and as you say he'd pair with Sims and replace nank perfectly in theory.
New rules should help too