It seems like instituting a reasonable ledge grab rule wouldn't effectively ban planking, but it would cut down it's use as a stalling tactic. Personally, I don't condone banning a particular strategy because it is hard to deal with, but planking to stall is an abuse of the system.
Planking ISN'T stalling. For like the millionth time, EVERY SINGLE CHARACTER can hit a planker. You can only stall if it's physically impossible to hit you. A lot of people plank with the intention to stall, but the tactic itself is not stalling
The thing that people are debating about planking is if it puts the opponent in too disadvantageous of a situation for it to be legal. For some characters, trying to counter planking leads to getting hurt and can possibly lead to a gimp. However, hardly anyone's actually tested this, and character boards haven't taken the time to actually bring the issue up. People shouldn't be complaining if they don't even take the time to experiment with planking and know the full extent of what it can do.
And a ledge-grab rule doesn't help. Usually, two scenarios happen.
1) Say you're a Kirby or a Diddy fighting a MK. Now these two characters have good options against planking anyway and can already beat it, but with the ledge-grab rule, the MK can only grab the ledge like 50 times the match, limiting its usage. Because of this, the MK can no longer use planking as camping or a forced approach, because they'd just run out the limit on themselves. Against characters who have counters against planking anyway, all forms of planking are eliminated, the "stalling" part and the camping part.
2) Now say you're a Falco fighting an MK. Falco, as of now, is known to have very bad options against planking, Without the ledge-grab rule, planking beats him. However, with the rule...planking still beats him. Why?
If the Falco just hangs out in the middle of the stage, the MK can just sit on the ledge and not regrab. Because Falco doesn't have an approach against planking, the MK doesn't have to worry about coming up to hit the Falco. Therefore, he's camping by just staying on the ledge.
Now when the Falco approaches, the MK regrabs the ledge and starts planking. Now, the Falco either gets hurt or he gets gimped. Either way, planking beats him and puts him in a bad situation, while the MK can steer clear of the ledge-grab rule. The MK doesn't have to keep regrabbing the ledge when the opponent is away, so he can save his ledge-grabs for these times and ta-da, Falco gets planked regardless.
Not only does the ledge-grab rule ban a tactic that's arguably not even broken (and even if it is, people haven't taken the time to find out, so I'm calling it not broken until they actually do), but it only helps a small amount of characters that kind of struggled with planking before. Characters who really can't do anything about planking, like Falco and the other spacies, Falcon, Ganondorf, etc., still can't do anything about planking even with the rule.
Edit:
A large portion of the cast can't do anything to stop a planking MK.
You know this how? With what research? How did you test this? Or are you basing that statement all on assumptions?
My point still stands. People need to actually test planking instead of just THINKING about what can happen against a planker.