Seems a bit too heavy handed.
Well how shitty does this forum have to get before heavy-handed measures become necessary? I would suggest that the benefits of a measure like this would outweigh any inconveniences experienced by some noobs who are in all likelihood alt accounts anyway. It's not a perfect solution, but it's worth trying. It's better than doing nothing. If you keep doing nothing, bitcointalk might as well start up a local board for English. Drives me nuts when proposals get shot down because they're not perfect. Nothing is.
The bounty board isn't the core issue. If all shitposting was limited to it, we probably wouldn't be talking about it. The issue is users using the pumped accounts outside said board and until that gets solved, enacting measures that only put extra burden on moderators is pointless. That's why I mentioned simply not counting posts and activity within such boards - stops the pumping and doesn't require mods to interfere.