Steel trellis. You can cut it shut it, change it, make it with less or more flex, move the engine about. Why on earth would tey go with an aluminium frame which tey know absolutely nothing about. They are sticking with the V4 which they know a great deal about.
current rumour mill has either FTR or Sueter working on a alloy beam chassis for Ducati to try. Ducati have no in house experience of alloy beam frames so have had to look outside of the company