I think Flavien said in last weekly report that alpha is delayed for a 2-3 months.
This is from update #52 which was posted at the beginning of March, so end of May is a possibility.
Update: from Keith in Update #55,
Needless to say the networking and UI systems have taken much longer than we initially anticipated for a variety of reasons that will probably be a blog post for another day. This means at a minimum we’re looking at another 2-3 months before we can ship the Alpha. [snip] To make up for the additional delay we’re considering the possibility of having 1 or more Alpha player weekends like we did in January