Im not shure wich Data Type we should use for the Objects.
I dont likethe  idea to keep all scripts, images etc as sepperate files, because than you have to zip / unzip the files if you share them.
And the problems that came up in other Clonk Versions already, the problem with changned packs.
If somebpdy make just a small change in a pack a) you have to load the hole pack b) if you save it you have a probebly buggy version of a pack

I know it dont fits to the "Open"
but i vote for a fileformat simmilar to the old ones (what i mean is one file per Pack)
And i vote for an index with signatures of projects so that its clear that it is an unchanged version

but if you want to change the Pack it might be possible with an patch that overwrites some objects.