As much as I like STEEM, the platform cannot natively handle smart contracts.
Steem Engine intends to solve that, but we don't have any major live executions on it to prove its functionality. The Trilemma proposed by Vitalik was referring to smart contract networks; STEEM is not a part of that list, at least not yet.
In fact, even the betting applications built on STEEM don't utilize smart contracts to deliver trustless interactions. Betting applications are the lowest hanging fruit for pretty much every smart contract network.