More FUD as usual. Apple is NOT intentionally and proactively killing these unlocked phones -- the company is simply warning that futures updates to the phone may render them inoperable. Apple has no reason to develop the iPhone updates in such a way that works around these hacks.
Additionally, there is already published information on how to reverse the hack, so anyone who wants to prevent this issue is able to.
Apple cannot void the warranty for any updates that are not actually putting the phone at risk. There is nothing hard-wired in the phone that should prevent it from operating on a compatible network. If anything, what Apple is suggesting (re: warranty voiding) seems blatantly illegal.
Additionally, there have been updates since the first releases of these "hacks" and there have been no issues with the phones. If Apple is now claiming that the phones may be rendered inoperable, there is little to read into that than those hacks are being specifically targetted.
Again, this seems a very strong-arm tactic and, once again, seems illegal.
However, the last line in the little snippet you posted suggests this may be limited only to the cards using other carriers SIMS. Given that the SIMs are using the same circuitry and general layout, I fail to see how using a SIM card from another carrier can cause issues.