You are right: the JUser BestBefore plug-in cannot do exactly what you want, because it does not interfere with the Joomla! user details management.
With Joomla! 2.5 however, you have the option to create additional (custom) user groups and with the JUser BestBefore Business plug-in, you can create two separate user group clusters with each their own expiry settings. As an example you could set the expiry for ‘normal’ registered users (cluster 1) to - say - 6 months and the expiry for a ‘special’ user group (to be created and assigned to cluster 2) to - say - 12 months.
Still, you will not have an individual expiry setting for each individual user. The plug-in simply doesn’t do that.
I wonder if the function that you are looking for is practically do-able. Would you be willing to assign an expiry term to each individual user? What if you have some 1000+ users? Just wondering… you will surely have your reasons…
PS: In Joomla! 1.5, you cannot create additional user groups and therefore, the above suggestion is not feasible.
