Counting available blank cells to calculate an end date

If a blank cell is populated, it is no longer a blank cell. Also, you do not specify the range you want the cells counted in, with beginning and ending cell. Please be specific about your parameters for what you want to measure. Based on the scenario in the attach file, you could simply add 100 to the starting date.

I agree, the wording is odd:

I need to know what the date would be when 200 blank cells are populated (starting from 08/05/2015)

Since, once a cell is populated, it is no longer blank. In an attempt to read between the lines, I think you want to know the date when the 200th empty cell occurs within your table. This equation will do it, but you need to enter it as an array formula by hitting CTRL-SHIFT-ENTER when inputting it.
=INDEX(B2:B31,1+MAX(ROW(A1:A30)*(COUNTBLANK(OFFSET(D2,0,0,ROW(A1:A30),10))<200)*(COUNTBLANK(OFFSET(D2,0,0,ROW(A2:A31),10))>=200)))

is it possible to do the same but rather than telling it which cell to use as the start point for the index (start date), instead have it work from the cell containing todays date??

This may be able to be optimized, but it seems to do the trick:
=INDEX(B2:B31,MATCH(Q2,B2:B31,0)+MAX(ROW(A1:A30)*(COUNTBLANK(OFFSET(D1,MATCH(Q2,B2:B31,0),0,ROW(A1:A30),10))<O1)*(COUNTBLANK(OFFSET(D1,MATCH(Q2,B2:B31,0),0,ROW(A2:A31),10))>=O1)))

Note, I made it a bit more generic:
Cell O1 holds the quantity you are looking for (e.g. 200). Just replace each instance with 200 if you always want 200.
Cell Q2 holds the start date.
Again, enter with Ctrl-Shift-Enter