There are many potential areas of concern but it is not possible to say which might apply to you based on the provided information.
One consideration would be communications delay and outages. Depending on the speed of your connection to the overseas system you may experience delays in system responses. This is assuming that the remote system has the spare capacity to handle your workload — obviously an undersized system would also increase your response time. Depending on the reliability of your network you may experience more outages due to communication failures.
A second consideration would be national language support. If you will be running in your own partition the remote system should configure your partition to match the system values (QCCSID for instance) and environment (NLV for instance) that you are currently running in. If you will be sharing the same partition with an existing set of users you may have globalization concerns (CCSID, date formatting, language translations, time values, Daylight Saving Time observance, etc).
From an operational point of view, you will also be dependent on the remote system operations staff for release upgrades, applying of PTFs, hardware upgrades, backups, etc.
Consolidation of iSeries (or System i) machines onto one larger central system has been done sucessfully by many companies. It does require planning in order for the consolidation to be done transparently from a user point of view.