I find this pretty scary. It may be "worse case" but when worse case happens by someone mining a single block and the result is a drop in the network hash rate by almost 50% and people lose money, that seems non-optimal. Depending on the make up of the pools that support it it could push one of them over 50%.
What percentage support by February 15'th would make you comfortable? As I said, if it is 55% from Feb 1 to Feb 15'th (or, worse, if it varies a lot in that time) then I think we'll need to re-assess. I expect to get well over 70% support starting Feb 1.
I'd rather use some common sense rather than spend days arguing about exactly what percentage aught to be specified in the BIP, or how many standard deviations of variance are acceptable between Feb 1 and 15.