The idea has merit, but also has quite a few dangers associated.
For the sake of argument a system is being traded all the time, except when the system is Long (as per the equity curve chart) it is traded for real, and when the system is short it is 'ghost' traded instead and no money behind it.
Running an essentially mechanical system I would expect to see a good hit rate and a good ratio between profit/loss. keeping a track of the systems performance is also necessary (that's obvious).
Moving on in my thoughts. Market conditions do vary and can go through periods of time when systems that are very profitable in one set of market conditions can become unprofitable in others, and obviously I have no desire to trade uprofitable systems. So knowing what type of market conditions generally prevail will dictate what type of system is used to trade it.
Analysing the equity curve from a system can be an early warning of a system starting to fail (albeit temporarily) and might save some losses. But there are other methods of ascertaining where a particular system is still valid and within the acceptable range of profitability.
On the other hand there is always the possibility that the set of drawdowns was temporary and factored into the system performance, and that the system goes short (i.e. from actualy trading to ghosting) just as it becomes profitable again and long just as the losers show up.
Even moving between different systems can be subject to this problem, although it can be argued that if you have the right system running in the right conditions at the right time for maximum profitability you would be increasing your overall results and reducing your risk.
So even Ghosting it can lead to always being in the wrong place at the wrong time (where choice of system is concerned). And it's a problem that gets compounded the more systems you have.
Now that is not to say that it is all bad news, because systems that are very heavily curve fitted tend to have a limited shelf life, or a limited number of times that they can be applied. They can be good in one set of market conditions but not in others. So keeping track of both market conditions and the results of the 'ghost' equity curve can identify longer periods where the system has greater profitability.
My thoughts so far are that it could be a good tool if used in combination with other tools, and with great care, but on its own carries quite a large element of additional risk associated.
Natalie