All owners of devices with iOS 4.3.5 or less, OS X 10.8.5 or less will have their payment information blocked and eventually your card will run out, so you will be forced either to buy new device or won't be able to use store.
As move is clearly can cause class lawsuit Apple presented it as measure to prevent some financial problems for users without any foundation.
It is rumored that Apple will move fast towards newer OS versions on older devices forcing users to buy new ones due to problems with stock that they have now.
Update: As noted by MacRumors forum member Cdbrawn, this change appears to be in line with the PCI-SSC's requirement that all businesses processing payments online must transition to TLS 1.1 encryption or better by June 30, 2018. The affected iOS, OS X, and Apple TV software versions use TLS 1.0.
Sounds strange as they do not prevent any "business transaction" after June 30, 2018. They just block ability to update payment info.
And making software update to TLS 1.1 is very simple.
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