I can't see Armada's table size and points restrictions being something that's set in stone, and strictly adhered to.
They will be by FFG.
FFG is not going to make anything that breaks the standard tournament format, so while someone may host a 600 or 900 point game on a 8x4 table and play with 3-4 ISD's per side. That is not something FFG is going to take into account when they design stuff.
In X-Wing they design stuff around a 100 point 6 asteroid death match. For epic they design stuff around a 3x6 table with 300 points per side. For Armada they're going to design the game around 300 point lists on a 3x6 table.
That means they'll make the ISD a size that works for the standard game, the model is too big for a 900 or 1200 point game on a 3x6 table is not an issue that's going to be considered.