Jetpack is a young project that is becoming more mature with each new release. I take my add-on, ContextMenuPlus as an example and explain the limitations.
The first limitation was preferences, I had to use three modules(“simple-storage”, “panel” and “widget”) to make Preferences available to users(ContextMenuPlus 0.4). But when the “simple-prefs” module landed in Add-on SDK 1.4, I implemented it as soon as I could(ContextMenuPlus 1.0).
The second limitation is localization. “l10n” module for localizing landed in Add-on SDK 1.5, but it does not cover everything. I could localize context menu items, but I could not localize preferences. So I decided to wait till it’s possible, because I didn’t want to localize just half of the add-on.
The third limitation is location of context menu items. There were 2 users that complained that they can not move the items(using Menu Editor for example – Update: Another user said that it is possible to move items using Menu Editor!) but neither can I! It is not possible to move menu items, not yet.
There are many limitations, you can not do whatever you want(using add-on SDK). As I said Add-on SDK is young and with each new release there will be more features and less limitations.
The annoying part is that users think Add-on SDK bugs and lack of some functions are add-ons’ fault :)