So I was looking for DreamArena artwork and came across this website, which appears to be a CV for someone involved in SEGA's DreamArena websites back in 1999-2001. Specifically this page refers to a DreamArena 2, where SEGA executives wanted the front page to include more content but be radical looking and imaginative, and it has a picture included with one of the potential concepts for achieving this.
I think it looks awesome! It also fits in with the European Jet Set Radio, Toy Racer and MSR website layouts. The description makes it sound like it was going to utilise the DreamArena mouse more akin to controlling a "character" on the site (likely a mouse overlay) and accessing content more like a video game. It seems the three aforementioned websites wound up a half-measure towards this plan, as they ultimately didn't include a "playable character" interface, but it sounds to me as if it would have been very cool if implemented.