Central Line trains are 20 years newer, so presumably aren't going to be at the front of the queue. They do seem to be planning to do major refurbishment / upgrades on them in the near future, up to replacing the motors and related power control systems (DC to AC motors).

Bakerloo line trains are about the same age of the Picadilly line, but the Bakerloo line is less used, so presumably that has edged the Picadilly ahead. They are next in line, as the article notes.