Hello,
It'd be difficult to add another voting option to SkyWars as your time is limited, I can tell from experience that I already find it difficult to vote 2/3 in time. Though if, let's say, this were added within one of the existing voting options or an external solution finds its way to make this suggestion work, I still have difficulties with it.
Let it be known that SkyWars isn't as much about fair combat, like the PvP game-mode is. What I enjoy about SkyWars is that people who don't practice their combat skills lifelessly still have a chance at winning and earning points. And the fact is that the Lava bucket is one of the many reasons why the game-mode is currently balanced. It provides people who aren't gifted at PvP or have worse armor to win the game, and removing this, as good as it may sound, will ruin the game more than you could possibly imagine.
If you take away the balance of a game-mode it'll quickly become available to only one group, in this case that'd be people who practice PvP lifelessly. In conclusion, removing the lava bucket would make the game unbalanced and ruin it as time passes by.