[DTV]

I fear that what will end up having, especially the long lead time to the end of Doctors, is the slot ceases to be drama and becomes low cost repeats. As you say there has been a reduction this year in drama in that slot and it looks like the second programme to share the old Holby City slot, which was supposed to be an outside London commission, is likely to never materialise.

Fundamentally and bleakly, it's all just accounting. Drama is expensive; continuing drama less so, but still costlier than non-drama replacements. Continuing drama also suffers from having less commercial return potential, so it's not as worth the investment, especially when ratings are no longer standouts. 

Nonetheless, I suspect the cut in new non-continuing drama hours/costs over the last few years is roughly similar, it's just less noticeable as it's not in a permanent slot.