it was the first time they had done anything like that.

I could be mistaken, but the No Time to Explain quest actually appeared before Black Spindle, but no one noticed it the first time. It was because Black Spindle made people accept the possibility, that people actually started looking for it and eventually found the parts.

because we hadn't had any hints they were doing it at all.

Maybe not that it would be a daily mission, but there was a hint. When you dismantle Black Hammer you get an item that, if I recall correctly, shows the icons on the locks prior to that door being open.

that they themselves think will be so obscure

I don't think a giant door being open for not dying is really obscure.

I was hoping maybe something like this is still in the game for us to find.

Considering Destiny has something like 20 million players, with a fair amount of them making income off things like this, it would have to be hidden really well or have extremely weird requirements for someone not to notice. There is simply too many people looking for things like this for them to stay hidden.