Any and every chain, so long as it is mutually beneficial and viable. But the focus is South Korea 1st. ICON already has blockchains running. One for a handful of hospitals, another for some universities (3, expanding to 13 hopefully by end of this year), another for some banks (5 or 6 IIRC, one of them is Woori Bank, and in development with Ripple Asia), and another chain for 25 securities firms.
These are contractual partnerships. ICON will look/work at expanding globally as soon as possible.
ICX is an ERC20 at the moment, after KYC and AML phase passes, mainnet launches. Part of the launch has to do with ICX being converted off/away from the ERC20 protocol and on to the loopchain (ICON Foundation native chain). This happens somewhere before the end of the year.