There are so many factors that come into play when trying to answer your question. You mentioned that on your recent visit you stayed 10 days at BLT, but you didn't mention what type of accommodations you had. If you are planning on getting only 200 BLT points, keep in mind that 200 points will get you 10 days in a BLT studio during most seasons, but won't get you even 7 days in a 1-bedroom during any season. You would have to bank and borrow to afford a 1-bedroom, or reduce the length of your stay.
One advantage of switching 300 BWV points for 200 BLT points would be in the MF savings. The BWV points cost $1,563/year, while the BLT points cost $734/year, a net difference of $829/year. No one can predict what the MFs will be 10 years from now, but if that difference continues, you might (hopefully???) save $8,290 in MF in 10 years. Of course, that "savings" comes at the "cost" of having 100 fewer points to play with.
I would take the advice of the PP and delay making the switch at this time. First, until BLT is sold out (and they have only sold about 41% of the points to date) there will be relatively more BLT villas available to
DVC members than there are BLT points in play. Thus, it should be easier to get a BLT villa at the 7-month mark. Second, no one knows what the demand will be for specific BLT views. It appears that Standard View is actually more popular than MK. Lake View appears to trails BLT-SV and BLT-MK, perhaps because there are far more LV villas than the other two. If you would be content with LV, then you stand a better chance of getting into BLT at the 7-month mark. And third, I suspect that within a year or two BLT resale contracts will be more readily available and at a much cheaper price that Disney's price. If you wait, you might be able to get 200 BLT points on the resale market for 10% or more less than Disney's current price.
Good luck!