I've just about finished importing the older islands, complete with the new sky, HDR lighting, and NO pop-up errors or .rpt errors. The main caveat is that I won't be even attempting to import the old soldiers, weapons or vehicles. The basic logic behind this is that you cannot simply import an A2 vehicle to A3 in a 1:1 manner. It requires a huge re-write of the config, and there is a very good chance that BIS will be doing it for us at some point anyways. But the good news is that you should be able to run an island designed for A2 without error (I actually did this to use wgl_palms). I'll try to include an addon that applies the new lighting and sky to old maps, as currently they will use their original lighting unless (easily) modified. Some might prefer the original lighting so I'll make it optional.
What I had to do:
Added a bunch of dummy cfgPatch entries for deleted pbos. No requiredAddOn errors
Removed a few hundred stringtable entries that were duplicates of A3 ones
Modified the faction and vehicleclass of a few warfare buildings
Privatized some public units, mostly from water2.pbo so I could use the LHD in Utes without errors
New sounds.pbo, A2 and OA only needed 3 sound files from the original
What needs to be done
Fix a .rpt error where it generates a long list of missing bones in OFP2Skeleton, probably from a vehicle cargo animation
Add new ambient life to the islands. The original animals aren't there anymore so I'll rebuild that with A3 critters and fish
I would like to try importing the A2 animals. I had a vision of ragdoll cows and satchel charges.
fix the intro missions so they don't use missing addons "can not play due to missing addon" message
update the streetlamps, they currently look like they did in A2 (no flares)
Well it does need a little more work, but currently you can start A3, load up an A2 map, make a mission, and play it without any pop up warnings or messed up UI. I was impressed that the older islands don't look dated at all, they look awesome in the new lighting and moving through some of the bigger buildings (like Devil's Castle) is really smooth with the new controls!