Sorry I was very busy and did not read well enough your post.
The arbitrator should never be active part of the trade, only if something goes wrong. Otherwise the arbitrator will become the escrow.
To apply your idea to the current system it would be that the 2of3 MS deposit tx will be funded by the seller only who will pay the funds normally required by the buyer (0.0112 BTC).
The take offer fee has also a not so obvious protection mechanism beside that the trading fees are revenue sources (now for the arbitrator, later for the Synergetic cooperation).
If the taker does not need to pay any fee he could harvest the offerers personal information which will be exposed in the last step in the trade process after the taker fee is paid and before the deposit get finished. Those data are the bank account data in case banks are used as payment method and carry usually the name of the offerer. So if we would allow the taker to take offers without fee payment they could build a manipulated version of the software and stop the take request after they received the bank details in that step of the handshake.
That might be a more theoretical risk atm, but better to care about such. Once Bitsquare becomes more relevant there might be a more realistical risk for that. Of course the taker fee is also not a perfect protection but it drives up the costs. Additionally we have other protection (network level blocking)...
And beside that it will never be secure and it might be that we need to stop it because people start to abuse it. The taker would have zero risk and nothing to lose (people are lazy and careless). Again probably not a problem yet, but once the platform is more relevant you need to count with more troubles....
But beside that conceptual point it would require a bigger change in the trade protocol and I don't want to change/add here anything if it is not heavily needed, simple to limit risks and effort. It is the core of the app.
I find it much easier to solve the problem by outsourcing it to a micro credit market, which - if there is demand - would be another feature of the platform.
As you have probably seen already that I started a thread for offering such a credit for newcomers.
I assume in reality there will not be much demand for that. But we will see.
Another idea is to add some kind of Reputation tokens (@mepistol has some ideas in that direction) which can be earned by providing proof of reputation and can be used as collateral for lending.
No concrete idea how that could look like but there might be some way....