Why would anyone buy STEEM? You don't need more than your 10 starting STEEM to post, comment or read stuff on steemit.
The only reason to own STEEM that I can see is to get even more STEEM by posting and curating content. If the price of STEEM remained steady or increased, that would be good enough.
However, there is a 100% yearly inflation. Assuming the market cap remains constant, that means each STEEM will lose half of its value by next year. That is a tremendous downward pressure: why would anybody invest into something that loses half of its value every year? Unless the market cap increases, but that brings us back to the first point: why would anybody buy STEEM with USD or any other fiat?
There is also another risk: even if you buy STEEM and power them up, you might end up losing more money to inflation than you will make from contributing on steemit, if you are a less popular than average contributor.
I really cannot figure out the economic model of STEEM.
If nobody has a good reason to buy STEEM, then the currently rising price is a bubble resulting from pure speculation. What is going to happen 2 years from now, when huge volumes of STEEM have been powered down and nobody is there to buy it?