I agree that they can be, but the question is how they will get there. We went through a version of this problem when Photobucket started charging for picture hosting. DQ had tons of very useful pictures in his DIY posts, but as I understand it, the mechanism to get the pictures released from Photobucket so that the threads could be preserved was for DQ to pay for the privilige of allowing us to review his pictures. Needless to say, the economics didn't work out on this (for DQ), and accordingly many of his old threads have Photobucket crap obscuring the pictures.
In this situation, we have a similar problem. For people who have only posted a few DIY threads, it may not be too much of a burden to move or link them to the new section of the forum. For DQ, however, it would be a big undertaking to go through the forums and move or link to all the DIY threads he has posted. He's already taken the time to puase work, take pictures and then after completion of the work go back and write up what he was doing and create a thread with both the written descriptions and the pictures. (Now, obviously, this helps document the work he has done on his car for future reference, but that's beyond the point.)
Indeed, the proposal that authors volunteer to move their stuff is likely to place a very heavy burden on those who have already taken the time to photograph and post their work (which itself is no small thing; I don't do it because of the time specifically dealing with the photographs). Add to this the fact that we may well have very good DIY threads by folks who no longer own coupes or are not very active on the forum. (Rob Siegel's excellent thread on the heater core bypass comes to mind.)
And so, I have a suggestion. Could we create a mechanism that allows members to nominate threads that they have found useful. This could be moderated in the same manner as the e28 stuff is moderated to ensure quality. Admins could, if they approve, either move the threads or put the links in the DIY section. My suggestion relieves the original thread author of any need to populate the new section with old threads, but leaves open the possibility that they could do so if they would like. And it solves the problem with people who posted good stuff, who are no longer active on the forum. And those of us who would like to see the new DIY section thrive could volunteer some time to find and reference threads we have used in the past.