So in a way, this could potentially screw the economy over for a few reasons. Generally, goods (Diamonds, Redstone, Gold, Iron) are close to lava, in cases hanging above it or below the lava, making swimming in it without damage only the beginning of easy items.
A lava suit would be interesting, but the issue with a lava suit is you would die within 3 seconds after the air runs out. Unlike water, its 2 hearts almost ever .3 seconds and with water its about a half heart every .5 seconds. So you would die fairly quickly. Obviously, the lava suit would have to lose bubbles above water, as theoreticly no one can swim in lava and it's just not minecraft.
If this was to be implemented, id say lava suits for $80+ donators, it's something that could eventually get exploited too, so if so many people had it, lava grief could go much higher than what it is now.
I think this is also a bit unneccesary because all you have to do is place cobble or any block and make a path. I will admit its a bit risky to do so, and I'll admit ive been in that situation before where ive fallen into the lava and almost died (Yay for Diamond Armor!)
In tern: The Idea is good, but I don't think its totally necissary.
EDIT:
I just confirmed that there is NO mod for lava suits or the ability to swim in lava in the official bukkit plugin list. The only way this would be possible would be if one of our devs volunteered to create this, and I dont think this is top priority at the moment.