I think that's a great idea. DU is the perfect game to do it in. Just think of meeting a new trade partner who started up his own trade route, he does a great job and is fast and friendly. You look up his company in the stock exchange and buy some shares because of the good interaction. He gets money and as he grows so does the stock value. Being able to sell shares of a company in transactions would really help businesses form alliances and trust with partners. You own 5% of the company who delivers goods for you, and they own the same. Both of you want to see each other succeed.
The hard part is getting a system in place that's not too complicated or easily exploited. Have a $ value assigned to each group, whether it be a guild, company, resource or corporation Base values like in the real world, off total value and demand.