Oh, I'd add Downlode Tales to my list - I know it was raised as a possibility in the podcast interview.
I can't remember how many episodes of DT there were - ISTR there were quite a few, but if it's too long for a single issue they could spread it over two or three volumes and fill the remaining space with Sinister/Dexter tales that have been skipped over in the proper collections.
And how about The Bendatti Vendetta?
There's a lot of scope for niche Dredd collections like the Bad Manners one a while back, or there would be if it weren't for the Case Files making them a little redundant - themed Mrs. Gunderson, Angel of Mercy and Slick Dickens compilations would be pretty sweet.
And what about Helltrekkers? I've never read it - dimly recall that it doesn't have many fans - but it's Wagner and Grant isn't it? Did the Meg already reprint it?
A proper Missionary Man trade has been suggested - I think one is scheduled for the US line for next year (presumably because of the Quitely artwork) - but if one doesn't materialize in the UK there's enough (popular) material there to fill plenty of Meg collections.
And what about material from outside 2000ad? I can't remember exactly what Rebellion does and doesn't own, but perhaps that is an avenue that could be explored? There's also Judge Dredd vs Predator and Judge Dredd Vs Lobo - two strips I'd like to see again but which wouldn't get a chance in the main trades, but again there's a rights issue there.