I understand the need for backwards compatibility but lets gets serious.
WordPress is built to work from PHP4 and higher.
It is built to allow all versions of WP from 2.2 to on.
This is A LOT of unnecessary bulk and work.
Seriously I just tried to upgrade from 2.3 to 2.8.4, guess what?
It didn't work...
This means that since there are discrepancies already in the core from version to version, I believe removing a lot of the bulk from backwards compatibility would be fine.
One subversion back is all I ask. (2.8 to 2.7)
As far a PHP 4 is concerned, I would like WordPress 2.9 or 3.0 to say goodbye to PHP 4 once and for all.
PHP 5 is much more suitable for Object Oriented programming and will make the community development much cleaner, useful, and all together wonderful.
With better plugins, it will increase usage.
It will also entice A LOT of people who haven't been upgrading to do so because well, it is forward thinking.
Listen, with Object Oriented code it is a lot easier to make updates and changes.
If you have an update to a Class then you change that class, not the entire application. Being built from PHP 5 you can utilize all it's greatness, and with PHP 6, 7, or whatever it will always be Object Oriented so no need to worry then.
There are classes at the base of WordPress but they are written with PHP 4 in mind, and are wrapped in what seems to be hundreds of global functions and objects.
I just think worrying about PHP 4 is holding WordPress back so much its sick.
I was so happy when the my-hack.php functionality was removed.
Lets see more of that!!!