Over the last few days, the members have all been posting things relating to the numbers 4, and 5, which has gathered a lot of speculation among keyaki fans on 2ch, s48 and twitter as to what exactly it could be. The only member currently to not have posted something like this is Hirate Yurina.
Some speculations are;
New single released on April (4th month) 5th
MV reveal for W Keyakizaka no Uta
Date they will reveal the senbatsu for their new (unannounced single)
Ukifune from S48 made a blog post with all the members who have currently posted about it (all but techi)
They announced that they will be revealing the purpose of the 45 tomorrow at 10am, which some fans realized the amount of days from the 1st of January to 14th February is 45 days.
Lots of speculation, but i'm sure something interesting will come out of this lol. I'm personally thinking it will be the date for the single, but who knows.