Having no centralized exchanges isn't an issue. The main problem for monero is that spending it on goods and services could be made illegal.  In which case, even if spending monero is completely private, selling goods and receiving monero for them it is not, (except on darknet markets).  This is a big problem for Monero. I can conceive that soon it will be made illegal to accept monero as payment for goods and services. Once that happens it's value is tied ONLY to dark markets.  That's not great.