A dragon would probably enjoy that much space - it would give you lots of versatility for decorating and set up as well. There's no such thing as too big of a cage IMO and you'll be able to offer more and varied enrichment for the dragon.
Blue tongue skinks are another cool medium/large lizard, sometimes they are hard to find. I think you may also be able to keep a pair/trio of ackie monitors - but I'm not sure how docile they are. Water dragons perhaps, but you'd need to make a waterproof area for a swimming pool and plan how to keep it clean.
Some of the smaller lizards and geckos can do well in communities, I think - you could make a really wild natural viv with live plants etc for some smaller lizards.