Cranfield cite two reasons for the front door choice - it would avoid making a double-curved skin door; so it would be cheaper. Also, and this seems a bit odd to me, it would be out of the way of the cargo loader's cab - are they all RHD then???
It will be a smallish door, 96x76 inches, and is currently only proposed for the -300. The -200, if proceeded with, would have a narrower door.
Good luck to 'em, anyway....if 146 values fall enough it looks like a sound idea.
The TNT 146QT's are here for the forseeable; no plans to get shot of them just yet - just as well really, as they are doing a good job of keeping Mrs.Nopax in custard powder and knickers!