Also regarding Midwife - Blandings is down in the BBC media centre as starting in week 3. I have that down for Sundays (the only other possible slots that I can see would be Saturday or Wednesday.) Blandings, Midwife and Ripper Street would certanly be too much period drama.
Blandings and Ripper Street could go together on Sunday night because Blandings will be going down as comedy rather than drama and I think it will be half hour episodes.
If Midwife starts too late it'll be in the Summer when viewership is generally down. If Mr Selfridge is starting a week later what will Ripper Street face in week two? Also RS is still a bit exposed in its scheduling.