Maybe a silly question, but if the concept of a stable coin is to maintain market cap (i.e. coin price) by dynamically altering the supply and/or demand. (e.g. Tether, Ampleforth) then what is the potential for a return on investment? For example, if USDT is always about $1 what's the upside of investing in it if the price never goes up?
The only upside is that you are hedging your funds when the price of BTC let's say is going down, sort of stopping the bleeding and losing much of your money because of the downtrend. So There are no profit to be made in a stable coin, hence the 1:1 to USD.
Another use of stable coins besides hedging against the volatility of bitcoin and altcoins is that if you live in a country where the currency is losing value every day due to inflation you can use stable coins as a hedge against them as well, that way you maintain your purchasing power while the national currency collapses, while that use is limited since the countries going through that kind of inflation are limited it is invaluable if you are in one of those countries and you are suffering the consequences of hyperinflation.