What if morphing com didn't cost metal?

Just time. You'd need to upgrade time similar to now, but it wouldn't cost any metal.

Why not?

It creates a threat that is more interactive than the current commander who can ward a few raiders and then becomes vulnerable.
Upgrading commanders seems like a popular feature for newcomers, but experienced players rarely if ever get anything beyond the first level for specific scenarios (regen, machine gun/shotgun...).

You'd just need to remember to check your commander every other 5 minutes to queue new upgrades.

I think it should cost energy

it would give more of a flow to the game, so you get that sense of how much energy you should have at a certain point.

would help with teaching the pacing of the game I think