only advantage I can see to this is if you can create a pool of lava by turning all the obsidian block into lava at once.. or maby a 3x3x3 cube because making a lava pit more than 1 block deep is like impossiable

 

Love the idea +1

 

I for one think it is a great idea! +1

 

When I need to do this, I powertool 'fill lava' to empty bucket. then hold down right and left click together as you fly or walk along and it will place lava everywhere you aim.

When the bucket is full, the right click places lava.
When the bucket is empty, the left click fills it with lava.

It also works beautifully with water.

 

Still sounds cool +1

 

Honestly, I use to do the opposite: whenever I want huge constructions of obsidian, I place a few water sources and then dump lava directly where I want the obby block to be, so I don't have to 1) drop water on lava, 2) pick the obby, 3) place it.

However, if there's people who would make use of it and it's not an implementation nightmare (as it seems), why not? +1

I want to add just a minor remark: if you drop an egg, you cant un-drop the mess on the floor to make the egg back. Lava is supposed to turn into obby, not the other way around. In the same way, iron ingots are supposed to be crafted into armor, not the other way around.
So, if we allow a bit of reversibility on the lava-obby thing (and I'm not against it), then I can't really see any good reason to be against this suggestion as well: https://www.ecocitycraft.com/forum/threads/suggestion-adding-the-salvage-skill-from-mcmmo.152843 (and if you think it would disrupt the economy, read the results of my tests on fishing yield, it's a few comments below)