It's not that easy in case of stocks like Tesla. At the moment you have some UIAs from third parties there that represent real-world commodities or also Shares in decentralised Enterprises. And you have so called Smartcoins. Look it up here:
http://cryptofresh.com/assets
Take a look at the Exchange here:
https://bitshares.openledger.info/#/market/USD_BTS
and find more infos here:
https://bitshares.org/

There are several issues to be resolved but the technology is there and in the case of bitshares it's quite an elaborate one (using the same Base-Technology like Steem) even though there are other projects trying to establish a decantralised Exchange.