I think mechs would be cool, and I've seen a few people ask for them already, but I just don't think that they'd be useful or even possible with the current tech in the game.
For starters, there isn't much a mech could actually do in this game that a ship couldn't just do better, even on the ground. Want to lift and move something? Tractor beam or a cargo lock frame could do the job on a ship. Want to take it into combat? Shot down by manoeuvrable aerial forces.
There just really isn't much you could do with a mech other than showing it off.
It also isn't entirely possible, while there are moving joints in the game, they just really don't have the versatility for any kind of legs or arms required for a proper mech.
I have actually thought about having mechs before for moon surface exploration, but I immediately realised I couldn't make them with legs, since the tech is not there, so I decided to design it with a hover bank instead (maneuver thrusters with YOLOL script), then I realised the arms couldn't do much, so I cut them off, I had to cut down the torso and head since it was such a big target, and I just kept cutting bits off so it would actually be possible.
Then I realised I just made a hover tank.
Rather than mechs, what could be implemented could just be different endo sizes, small endos, big endos, wide endos, thin endos you'd have to give them all some kind of unique stats so they wouldn't be pointless, but it would be interesting to see.