Is the timing finally right for ETFs that invest in the “frontier markets” — those markets a tier below the emerging markets? There’s clearly a case to be made for their potential investment returns. Yet timing here as elsewhere can be everything: Several frontier markets ETFs that were launched in late 2008 ran aground on the financial crisis not long thereafter. Still, two of those have survived — The Guggenheim Frontier Markets ETF (FRN), from Guggenheim Investments of New York City, and PowerShares MENA Frontier Countries Portfolio (PMNA), from Invesco PowerShares of Wheaton, Illinois. And now the 800-pound gorilla has walked into the room. In mid-September, BlackRock launched its iShares MSCI Frontier 100 Index Fund (FM). The fund will invest in equities from 20 widely dispersed and very different frontier markets, from Nigeria to the United Arab....