I'd like to see all greater rifts become big looping tracks with intermittently dispersed elite packs that trigger a checkpoints on clear. Maybe throw in some little nooks to hide in, but nothing deep enough to divert the player from the main track.
Every third of the progress bar completed, the current floor despawns and a goblin portal to the next floor opens next to the players. First third of the bar you get a level with mobs from act 1-2, second third of the bar you get a level with mobs from act 3-4, last third of the bar you get a level with Act 5 mobs. After the last third of the bar the rift guard spawns as usual.
This would really level the playing field and I don't think circular tracks would make it anymore boring than it already is. If anything the uniformity would making greater rifts more competitive and a more reliable gauge of character performance.