It looks like it's built for the military but you raise an interesting point. Maybe someone could build a suit to make it slightly more difficult to run without creating additional ligament strain.
then why not run faster or further? regarding the ligament strain - this contraption adds 5kg to your weight, so i'd say there's some (tiny) additional ligament strain. i.e. the suit would just be a runners back pack weighting 5kg. fill it with water and food and you get a lightening load over time/distance too.
If you had a suit that could help increase intensity, you'd have way more possibilities. For example, let's say you wanted to train for a 5k. Generally, you mix interval days with just running 5k's. Those 5k days, you're going to be running as fast as you can at that distance already. If you had something to make it harder but still the same distance, you essentially feel lighter on race. It's a completely different feeling than just trying to run faster. People use weight vests or ankle weights for these things but they cause long term damage.
Generally, the best thing to do now to accomplish the same feeling is running on sand or inclines.
Wear a weight-vest. (Although that's probably going to increase "ligament-strain" somewhat, but I don't think it's possible to make something physically harder and not increase ligament-strain.)