Kodak shares have tripled after the announcement. It won't be surprising if other companies follow the trail, but as other people have pointed, it's a free market which means you can not stop anyone from entering.
Anyone can enter, but shouldn't exchanges list coins that allow everyone to mine? I mean the company itself can mine its own coins with other mining pools. They are going to regulate cryptos so hard in future, Wall Street and the Nasdaq stock exchange have listing requirements, while our exchanges don't have any, but you now want to hand these big corporations everything for free...? Do you think that your purchasing power can compete with Wall Street and the Nasdaq and with every other big business listed on the entire world's stock exchanges for ASICS and GPU miners? OK... we will see...