I think what #[6] means is by not having custdy you don't have the means to settle to the base chain trustlessly, through layer 2 onto layer 1 because the mint has to cooperate
Discussion
It would be different if the ecash secret or signature would actually be something you can use to redeem something on LN or the main chain (pre-signed tx maybe?).
Haven't spent much time thinking about it because we're too busy buidling with what we have so far.