While mechs aren't just big power armours, I'd think that the simplest one of them are just that. I was trying to make use of a power suit for carrying heavy weaponry and came to conclusion that no weapon was heavy or big enough that they kind of required a specialized suit to carry. Any half decent soldier type could just hoist just about every weapon anyway and at the same time the ship weapons are too big already and way too powerful as is for what I was thinking.
I felt that the game could use a weapons category in between the personal and space combat weapons and thinking about it, it would probably fit as 'vehicle size' weapons.
As for other mechs than just my boring artillery toting suit, I could see all kind of mechs having a place in. Whether it's battlemech style mechs whose role is like that of a main battle tank as mobile armored fighting unit to very high tier gundam like mechs that can do just about everything and anything.