Older versions would be incompatible with new saves, but Powder Toy can always successfully load saves with a smaller resolution (stamps, for example, are just saves with a smaller resolution).
I don't think the window will be made bigger any time soon - Powder Toy runs quite slowly enough already.
I don't think we'll be adding more work space. The server is low on memory already, and we had to cut down on how much history is saved for creations (5 history reverts per save).
@PizzaPlatypus The code for loading saves and loading stamps is the same. I have just tested increasing the resolution and it works fine with existing saves, apart from save thumbnails (which don't currently check the save resolution).
Edit: @LockheedMartin - I thought that was a problem with the sheer number of files, rather than their size?
Anyway, the point about bigger window size making Powder Toy too slow still stands.
@jacksonmj Last I heard was we limited history because the memory left in the server was 20mb. Each file, if increased size would probably need more bits and memory per file to compensate for the more pixels.
@Lockheedmartin Naw, naw, naw. There's plenty of space on the server, the issue (which has now been resolved) was caused by the massive number of files.