Q:
Questions about the "new" Lingering Curse.
A:
A1: Yes it is BASE Duration increase that means you can slap another 100% on top of it.
A2: They could, but Arena Net has then to decide if it is working as it should. Basically it should not affect Sigils, because their Conditions are not applied by the Scepter Skills but by themselves and LC talks about “inflicted by scepter skills”