[joeysteele]

They should either have vote to evict or vote to save for all series, it still depends on how many housemates are up for eviction in the first place.
If there are only 2 or 3 up, then vote to evict or vote to save doesn't matter since it is virtually a vote to evict anyway in that scenario.

Vote to evict opens the door to organised voting to get a housemate out,vote to save makes that task a lot harder when 4 or more housemates are then up for eviction.

It is an interesting idea in the opening post but I agree with Mock, it would be likely confusing for the viewers voting.
For me I prefer vote to save and it is time they decided on either vote to save or vote to evict for all series.

I doubt they would get many celebrities agreeing to go in if their series were vote to evict however.
I think celebrities don't mind 'not being saved' in preference to having people actually voting to get rid of them.