I'm not sure it's that simple. Think of it in terms of shares in a company. When Apple does well does any executive sell their shares? Maybe, maybe not.
Nothing is preventing this musician from selling their MusicianCoins. If there are enough coins and enough musicians it won't do much to the price if the market knows how to value the coin properly. The musician might simply end up losing out on a profit by this action. Depending on the situation, maybe they might end up annoying the group and getting kicked out, who knows. It shouldn't be an issue though, just as it's not an issue with company shares.
But there's a difference: Apple shareholders don't see their shares redistributed at a steady pace - Apple shares don't have a built-in basic income.
The reason why I think even a single exit might do a lot to the price of MusicianCoins, is that financial success (not only in the music industry) seems to follow some sort of power law: a very small number of members amass a large part of the wealth [1].
Do people behave like this in real life (ie abandon their group when they strike success)? Well certainly not most people - men like Warren Buffett and Bill Gates haven't taken up citizenship in some tax haven to opt out of US taxes - but IIRC one of the Facebook founders did.
There are at least two reasons why it may be a bigger problem for MusicianCoin than it is for the USA: 1) the group size is bound to be smaller, so a single such event would cause a bigger shock, and 2) it's a much easier decision to sell your crypto-coins than it is to move country.
Of course this is all arm-chair economics on my part, and I actually hope you're right that in practice it's not such an issue - I love the idea and would love to see it work well.
[1]: see these sort of numbers, where the top 1% pay 23% of taxes: https://www.vox.com/2015/4/14/8406445/tax-state-local-distri... - and I reckon what would have been really interesting is if they had broken it down to how much of that 23% is carried by the top 0.1%
I'm not sure what you mean? If I hold more shares, I get more dividends. That's not redistributive, unlike what groupcurrency proposes.
Edit: ah wait, I think I know what you mean. When I wrote they have "no built-in basic income", I meant "no built-in Basic Income" - as per the context of this thread.
Nothing is preventing this musician from selling their MusicianCoins. If there are enough coins and enough musicians it won't do much to the price if the market knows how to value the coin properly. The musician might simply end up losing out on a profit by this action. Depending on the situation, maybe they might end up annoying the group and getting kicked out, who knows. It shouldn't be an issue though, just as it's not an issue with company shares.