Probably when more people join as full members and pay dues. That way the Group can afford to buy more disk space from the ISP. I don't deal with that stuff, but it's my best guess.
Naaah... I don't think I'll ever increase the size in the forum. If you want to upload a big file, stick it in the Technical Manual. It's probably where it belongs. There you can upload large files. However, best is to add the content to the Technical Manual, as then it becomes searchable.
The reason I don't want to increase the size in the forum section, is because it is not necessary. A picture can be made exactly right for forum viewing and still be in 256K. There's plenty of examples of that.
Bigger pictures ruin the browsing experience (more scrolling), and we still have a reasonable number of people visiting this forum with dial-up lines (notably JA17 and Dr Benz) who would not be well served with bigger uploads.
Peter