I guess the right thing would be to instead have it disabled by default in /etc/laptop-mode/laptop-mode.conf, and stop looking in /etc/default/acpi-support. For upgrades, this means people who had enabled it in acpi-support will have to reenable it in laptop-mode.conf, unless we do some ugly magic. Maybe a pop-up warning during upgrade will do, or the suggested logic below?
old acpi-support, old laptop-mode.conf -> upgrade action - reason:
1. disabled, enabled -> rewrite to be off (to preserve behaviour) - this was the unmodified configuration in Ubuntu
2. enabled, disabled -> do nothing (default off) - the user had done what we'll do now
3. disabled, disabled -> do nothing (default off) - the user had turned it off at some point
4. enabled, enabled -> do nothing (leave on) - the user had turned it on
(I am only talking about _ON_BATTERY here, we don't touch _ON_AC which was off by default anyway)
More sophisticated would be to detect if the user ever edited the configuration files, and ask accordingly.
Note that we have to leave the setting in acpi-support until laptop-mode-tools performs the above logic, which it should do only once. Then acpi-support can itself remove its obsolete setting, but only after it knows acpi-support has been upgraded and done its logic.
Or just let people read the Release Notes properly as they should :)