Ok, first off, this is sepculation on my part, I've got no info to back this up, but I'm gettig a strong feeling that June is going to see the summer of fliers. My reasons
1) Last June saw the release of spearhead (not that anyone played it)
2) Over the last 6 months or so GW has set a precedent of announcing its forthcoming releases several months in advance. For example we knew Tomb Kings would be the may release back in Feb and they did similar for BA, O+G and Grey Knights. Yet we are now in Mid march and have no idea what is coming June, which we should have given the pattern over the last few months. If its a new codex/army book why not announce it like the others? My conclusion is either that a) they don't have anything significant planned (extremely unlikely) or b) it is something they are keen to keep under wraps that is not a codex or 2nd wave.
What do the rest of you think? Has anyone got anything more concrete to back this up/disprove my theory?