So you want to make your old WordPress themes compatible with newer versions of WordPress. With WordPress 3.0 right around the corner, theme compatibility is something on a lot of people’s minds. It’s pretty simple: do absolutely nothing.
I’ve been making WordPress themes since around WordPress 2.3 was released, and guess what? Those themes still work today and there’s nothing I need to do to keep them working with newer versions of WordPress.
- Will they have threaded comment functionality (circa 2.7)? Nope, they probably still have “single level” comments though.
- Will it use post_thumbnails to handle post thumbnails (circa 2.9)? Nope, but not every theme makes use of post thumbnails anyway.
- Will they have the new navigation menus, custom header and background images introduced in the upcoming WordPress 3.0? Nope, and keep in mind not every theme will have a need for custom background or header images.
Most of these features I would consider optional. With maybe the exception of threaded comments or the new menu system, a lot of themes won’t even need or be designed around things like custom post thumbnails or header images.