If Villeneuve returns, that would be five current or former world champions competing. How long will it have been since there were that many current and former world champions competing?
Even four, sans Villeneuve, would be a high number.
Last time there were 4 was the 1999 season. Schumacher, Häkkinen, Hill and Villeneuve
Last time there were 5 (arguably) was the 1985 Australian GP. Prost (who was uncrowned, but had technically already won the championship), Rosberg, Piquet, Lauda and Jones
Please correct me if I'm wrong.