*
1. Legalize items and keep MK
Why do I think that items are the solution to the problem? Take a look at Jack Kieser's Items Standard Play thread to look at what they currently consider legal items.
http://www.smashboards.com/showthread.php?t=164675
(Sandbag) (Food) (Warp Star) (Bunny Hood) (Beam Sword) (Lip’s Stick) (Star Rod) (Super Scope) (Fire Flower) (Motion Sensor Bomb) (Freezie) (Smoke Ball) (Pitfall) (Mr. Saturn) (Green Shell) (Banana Peel) (Franklin Badge) (Screw Attack)
With the following items available as Counterpick items (read the thread if you're confused about the idea of Counterpicking items):
(Assist Trophy) (Dragoon) (Metal Box) (Home-Run Bat) (Hammer) (Ray Gun) (Cracker Launcher) (Gooey Bomb) (Hothead) (Spring) (Unira)
Now, considering just the items on random. How could these items collectively change the metagame enough that MK's Planking isn't an issue? Instead of going through them one by one, just look at them enough to see how many of them can be used to SAFELY combat 1. A character on the ledge, 2. A character in the air, and 3. A character under the stage.
The only major problem there is #3, none of those items can effectively combat a character under the stage. Of course, through the beauty of Counterpick items, Hotheads (or Dragoons, maybe) become situational but effective anti-scrooging options. However, this all relies on random spawn, right? Of course, but you have to consider that merely by stalling in a manner that prevents you from reaching them, there's a 99% chance that they're also giving up the opportunity to grab an item before you. This actually gives
decisive, fullproof ramifications to avoiding combat on or off the stage. And I'll leave it at that.