Yes, it has been asked for not many times but already years ago ;-)
The point is, that there might be blocks which should be there, e.g. for legal reasons, like disclaimers etc.. So noone wants to see that really as a prominent element of the page when first entering.
After the fiest time, a collapsed block stays collapsed, so it does not matter anymore.
IMHO if there is a tag "collapsible", it seems logical to have a tag "start collapsed".
Sorry, I was not aware that is much work.
I will have to live with it, just it was a NTH