As you know, sprinting is added to the game. Currently, you can sprint as long as you want, the only thing limiting it is the fact you need to be on a moderately flat road, and it bugs me a bit. Adding a stamina-bar to limit the amount your player can sprint might be a good addition. Jumping, digging, climbing up hill and swimming should also be limited by it. If you run out of stamina, your normal walking and dig-speed is cut to half, you can't jump or swim, which will cause your character to drown. The player will also start wheezing and breathing VERY heavily, infact so heavily other people will hear it.. Crouching and staying still will regenerate stamina faster.
Why i think this is a good addition:
-Makes bridges necessary when crossing big lakes/rivers
-Makes tunnels necessary for quick mountain-crossing
-forces people to work together while building a bridge or tunneling ("Cover me while i build this bridge.." "I'm out of stamina, you dig while i catch my breath")
-Increases realism. (Inb4 videogames aren't supposed to be realistic. (Inb4 OP can't say inb4))
Why is think this is a bad addition:
-Sudden increase of raging retards. ("ZOMG STAMINA RUN OUT SO QUICLY!! AD MOAR STAMI_NA!" "WY KANT I SWIM TROUG DA HOAL MAP?! STUOPID GEAM, COD WAY BETTAR!!")