What kind of business could be expected to yield reasonable ROI in bitcoin?
The main problem is the highly volatile exchange rate. Typical "real economy" businesses need your investment to buy manufacturing equipment and raw goods, which are both typically paid for and evaluated in fiat currencies. They produce goods or services which are also either sold for fiat money, or at least there is sufficient market pressure to adjust the bitcoin price so that its value in $ or € stays more or less constant.
For example, if you were looking for server hosting, the companies offering bitcoin as a payment option can't really make their prices much higher than comparable companies who take fiat money. So when the exchange rate goes up by 10 percent within a month, they would need to reduce their hosting fees by 10 percent to stay competitive.
Unless the business model has very moderate capital investment requirements and very limited costs for raw goods, it's hard to make it an attractive investment.
Businesses that could work are mostly using just digital infrastructure and consume and produce digital goods, for example exchanges, mining operations, gambling sites. Incidentally, those kinds of businesses have actually been relatively successful in the bitcoin economy. However, even those businesses have fixed costs (server rental and/or energy, employee wages) so they need real growth to generate stable profits.
If you look at a traditional share model where shares are freely traded, you need to consider that shares are typically evaluated based on two factors: Value of the actual assets belonging to the business, and expected future dividends. If the value of the assets is very low, the value of your share will almost exclusively depend on the expected future dividends, and this can fluctuate significantly, which hinders easy trading.
Onkel Paul