The Astros actually have a top rotation right now with Verlander, Keuchel, McCullers, Morton, McHugh. If they are thinking about a top of rotation starter, it would seem to be a move geared as much towards next year when they lose Keuchel and Morton as it is for this year. But if they are looking at Arrieta or Darvish who will cost a ton, why not just resign Keuchel with that money?
The list of available quality relievers is shrinking very quickly, particularly if it is true that Holland is going back to the Rockies. The rumors that the Astros are thinking about resigning Liriano trouble me.