I think giving this great-looking weapon to the Soldier would really bring out the full potential of this kind of weapon. Bear with me.

The unique nature of javelins opens up the possibility of "pole vaulting" with the weapon as a low- or no-damage form of rocket jumping. The concept is plausible enough to be intuitive - the Soldier's "jam rocket into gound and jump" vs. the pole-vaulter's "jam stick into ground and jump". Think about how much fun that would be, jumping into the sky and raining spears from above, like a Final Fantasy dragoon.

In exchange for losing splash damage, massive penetration. Kill your target plus the Medic behind him, pinning them both to the wall in an sweet, intimite shish kabob. Sniper can't do that, not with those tiny baby arms.

In particular, this type of weapon is a great way to open up the Soldier as a fun and effective class in Medieval Mode, and would go a long way to making Medieval Mode in general much more fun and dynamic.

Plus, one of the big draws to using javelins is that they can be used as melee in a pinch. This could have a thrust or short charge alt-fire, making the most of this kind of weapon and fitting perfectly with the front-line, mid-to-close range nature of the Soldier. This particular nature of javelins doesn't fit quite so well with the stand-in-the-back nature of the Sniper.

Just my two cents. I think this is a great model and an interesting new concept to bring to the game, but in my opinion the Soldier would elevate this to true greatness.