While I have been working on CPG 1.5, I recently started recoding some plugins and writing new ones. One of the major things that have been coded is the addition of quite a lot plugin hooks. While sometimes it is easier to create a mod (modifying the core code) then a plugin (no changes needed in the core), it does pay to create the plugin. It is easier to maintain and certainly easier to support. Plugins are portable when doing an upgrade, while modifications have to be applied everytime.
It is possible to convert every mod to a plugin in the 1.4 series, but it certainly was not always efficient. You could/can use the ‘page_html’ filter to change every aspect of Coppermine if you want to, but it would be quite resource intensive. Now with the additional hooks I was able to create a plugin to add an alternate CAPTCHA then the default one built in. I was also able to convert my lightbox mod to a plugin with the addition of an administration menu, no need to edit the files anymore!
It would be nice to see people convert their mods to plugins as it is more likely they will work on future versions of the 1.5 branch and possibly even after that.
I think over 90% of the mods currently available are convertable without to much hassle. It does take some time to get used to the plugin API, but there are enough plugins available to peek at their code and see how it works. The 1.5 plugin documentation is currently being improved, and I will add all my plugins in there with detailed info on how I wrote them.