If every country invested %1 of their reserves of bitcoin... im not sure what the price would be, but I suspect it would be high as fuck.
If that's going to happen in a further developed stage, it probably will result in the majority of the people to not even be willing to liquidate their holdings anymore. Seriously, if the current market has taught us one important thing, then it's the fact that selling Bitcoin has been an utter bad move. Sure, traders will always buy and sell regardless of the price, but those who know how to play the game, will always end up increasing their coin count. At some point we might even experience a time where people don't want to accept fiat for their coins anymore -- Bitcoin disconnecting itself from fiat, now that's something nice to focus on.
It depends. Will you be able to buy real state with bitcoin? if yes, then I guess people will have an higher incentive to hold. If you want to diversify your Bitcoin position into some real state, and by then it's still extremely difficult to find a good deal paid in Bitcoin and everything legally, then there will be an incentive to sell some of that Bitcoin.
We are going to find out in the next 2 years im afraid. By 2020 regulations should be more clear in how governments deal with bitcoin and acquisition of real state. Until then, the only sane thing to do is hold 100%.