Usually the answer is no on this because Steam makes a developer pay for each key they produce to avoid mass fraud. Meaning giving a Steam key for a Itch purchase is in a way giving 2 copies of the game for the price of 1 at a lossSee dev response below, I was wrong
Sorry but this isn't true. Developers are not paying to make steam keys. But to answer the original question we won't be transferring ownership from one store to another. If you buy on any store you will have the exact same game any other store has. If you want it on steam then I'd suggest waiting for the steam launch there.