im not from mananna base, but like with each currency, in the end people use currency where they have easy access to. If manna grows it can become more easy accessible then bitcoin.

Further Mannabase, could allow saving accounts for example:
Give 100% interest on your Manna up to lets say 10 dollar per month.
In this case people would have an incentive to hold some manna, but still with the monthly limit, the distribution would be fair in the long run.