If the Naysayers are right and there won't be an SSD, then I would be outright disappointed if the ISD will be the biggest (canon) miniature in the game. I think 8'' is too small for the biggest threat in the game.
Which is why I think a 2' SSD would be a reasonable model which is still playable (Most vids I've seen of people playing Armada, they barely use the full 3'x6' play area, most cram all shipsin a 3'x3' or even 2'x2' area). Don't expect it to be a valid tournament option, but enough casual gamers will want to buy it and will adjust their play area to accomodate it (like 4'x8').
The official tournament rules dictate a 300 point game and after wave 2 a 400 point game, yet there are many people who just want to have (more) fun and play 600+ and even 1000+ games, because they can and want big epic battles.
I don't see why a massive 2' SSD wouldn't fit in such a game.
I can easily imagine a 1000 pointish game where 1 SSD + 2 ISD and some 300 points of smaller escort ships will have to repel a (surprise) attack by a rebel fleet consisting of 5-7 MC80's and 300-400 points of smaller ships.
Sure it might not be 'canon' realism in terms of size, firepower, but this game isn't 'canon' realistic anyway (a corvette already has too much firepower compared to an ISD)
If FFG release a 2' SSD and you don't like it, either because it's too cumbersome to play on tournaments or too small to be 'realistic' then don't buy it. I bet there are enough people who will want to buy it and adjust their games to accomodate it.