This is sort of an idle thought that I'm tossing out there, but what if you could level up doing stuff with an overweight pack?

I don't think it would be good to do away with the overweight stamina debuff entirely -- after all, there should be consequences for deciding to walk around with one hundred crates, or five hundred logs, or whatever ridiculous thing you've decided to put your poor character through. But, if this is even programmable, it seems like all that time hauling around that weight should do something good for your core muscles (at least until you bend over wrong and give yourself a hernia):

-As far as I can tell, the stamina cost for each activity increases proportionately to the amount by which your pack is overweight.

-If introduced (and programmable), it seems reasonable for the new skill to increase similarly proportionately -- that is, higher overweight amounts ought to cause you to accumulate more experience in Overweight Activity (but by a very small amount, since we know that there is a wide range of overweight weights at which people try to do things on the Island). Perhaps in a nod to physics, there could be diminishing skill gain returns past a certain arbitrary point of overweightness (maybe your weight training with a 300kg pack is the 'sweet spot', and you get less Overweight Activity experience from anything above that, because of the risk of tearing your muscles apart, or something).

-The extra stamina cost from doing anything with an overweight pack would still apply. But maybe at Lvl100 Overweight Activity, that cost would behave as if your pack were 1-2% lighter than it actually is?

We don't exactly need this, but I find the thought of a skill called "Overweight Travelling" hilarious, so I'm voting in favor.

I love this idea! I am totally for this.