It might not be stable now but there's no reason why it can't stabilise in the future. Bitcoin is still relatively new and unheard of idea to most of the world so it will likely just be seen as a risky speculative investment for a while yet but that can easily change over time.
Bitcoin is a long way from becoming a currency you can live your life in. You also only have 7 transactions a second. But that doesn't mean Bitcoin isn't immensely valuable as a medium-term and long-term store of value
This can and will be changed. Bitcoin can scale to meet the demands of growth (though getting consensus is a different matter).
It will stabilise to a degree but like other assets it will never be completely stable. As for scaling we can be hopefuly segwit, higher block sizes and lightning will help but it remains to be seen if it will actually scale successfully yet.