Trading should be easy and fun, fun even if you lose by doing it. I even stopped using CCEDK after faced too many problems with them (also by my own mistakes).
Trading on OpenLedger is pretty easy. It is just like any other online exchange. You can use the web interface or run your own local client.
OpenLedger looks very good, but you cant deposit/withdrawal there FIMK or Bitcoin directly (same goes for NXT AE).
It works exactly the same as any other exchange. You send BTC to them and they hold it. They then give your account a positive balance, you trade, etc. The BTC never moves until you withdraw. OpenLedger works the same way. You deposit to a gateway, they give the represented token and you trade away. Another benefit of OpenLedger is that there are multiple gateways. If you don't like a particular provider, you can use another. It is like having multiple traditional exchanges all on the same inter operating trading platform.
If you can do gateway, you could do it also for some other coins what do you prefer, I bet it would became popular, at least for some groups at first and maybe for bigger audience later. You could make some money by transaction fees. I know it would take lot of work and at least one VPS server, but.. Just a thought
I already have a similar setup for my forging pool. I would only need to write the code to move assets around in OpenLedger. You are right, I could do the same thing for other currencies. It comes down to time and trust. I would need the time to write the code for other currencies and I would need to build trust from that currencies community. I hope that I already have the trust of the FIM community.