As financial models go, I think it's actually a slight improvement
Their financial model has always been badly broken, but this is actually a tiny bit of improvement. Well, maybe not, since they are putting the cart in front of the horse. Yes, they should ask the users what they want, but in a way that has meaning.
My long ignored suggestion is that they sell virtual shares on a by-project basis. The projects might represent individual features, or groups of related features, but the money wouldn't be released until AFTER enough donors had indicated that they really wanted to vote their wallets that way.
I'm sure there are many ways to implement this, but my version would be like a kind of charity brokerage, with the broker holding the money up front. That would be the Ubuntu organization in this case, but there would be no risk for them since they would be holding the money already.
You can argue that there would be some risk to the donors, since they might not find any projects that they want to fund, but that wouldn't be a major problem for two reasons. (1) If a donor picks a project and it doesn't get enough support, then that money would go back to the donor's balance and the donor would get to pick another project. (2) There is always risk in donating to a charity that might fail to complete it's objectives.
I do hope that Ubuntu succeeds, if only because Microsoft and Apple are mostly evil companies. However, they have working economic models, and this thing with the slide bars is NOT yet an adequate response. As for me, I'm still running Ubuntu on a couple of machines, but the utility has steadily declined over the last few years, I'm not using it for any "production" work, and at this point I won't miss it.