Does it make sense to try developing a system/strategy which would work with many of the major currency pairs, or a strategy should be developed for one pair only? As for today I do not see a way to develop a reliable system for multiple markets. Usually it works extremely well with one market and gives a fair performance with others. Thanks.
I would never trade a system myself that only works on one (currency) market and not on other currency futures. Ideally, it works not only with currencies but also in other markets (meats, metals, energy etc.) - maybe you have to change a few parameters but the basic idea should still work.
I agree, if your system works only on one market and not on other markets of the same family, don't put real money on the line. It means you over-parametrized and you curve fitted your system to the data you have available (normal mistake by the way) and the ''optimal parameters'' that produces the best profit etc are just a coincidence. What will work on all markets will be much more reliable to put your money on the line. Otherwise you will tank your account the second the market conditions changes,.