One fo the advatages of the WAAS and LAAS systems (as proposed) will be multiple glideslopes to the same runway. A heavy would use a standard 3.00 degree glidelsope and a 737/A320 could be placed on a steeper 3.10 to 3.60 degree glideslope with the same CAT I landing minimums with different threshold crossing heights keeping the smaller aircraft above the wake turbulence and reducing in trail separation. This however would only apply to airports that don't have any terrain issues. It's not quite there yet, but it's coming.
The same would apply to parallel runways. One at one slope, one at another allowing closer spacing (2,500' vs. 4,300' with terminals between the runways), unless of course you need both runways for all types of aircraft. But that just leaves a ton of wasted space between the runways when you figure the taxiways and terminals would increase the airport footprint to 4,300' anyway.