exept you are forgeting the main goal of Yoshida, make sure a maximum of people have done the content they have added soo far. people will not really come back to BC2-3 when Heavenward will be out, then the best way (without add echo) is to take out the lock out, since anyway, at best 1-2 month after the part 2 the expansion will be out.

just a reminder, heavenward is still announced for spring 2015, meaning before june. with the part 2 out at the end of march, it leave 2 month.