I can easily say my favorite and most memorable games i had in TA happened on the full metal maps, this is mainly because of how fast things move at the games startout. It was definitely a bit disappointing not too see this is supreme commander and again would have been some of the best maps for faster paced action without the need for modifiers. PA really has a chance to do something unique with this again. I am talking about the occasional metal moon, asteroid, or even planetoids adding in a seductive expansion point that could be a game winner if you can hold it. Instantly this reminds me of SC2 with the HIGH yield nodes, hard to keep yet rewarding. Another cool idea is having some larger metal patches which would again be a very good resource rich area for control. Areas meaby big enough to fit 5-10 adv metal extractors. In say a 4v4 these (properly placed away from any players start) would make great combat areas. Full metal starting planets may also be included as an additional option when making a map or starting a game.
There will be metal planets and options for the world generation as you want. Also mex points are currently clustered in resource rich areas.
Do note however that the current info on metal planets do not support comparing them to TA metal maps. The description of metal planets is battle-space-stations long dormant that you reactivate, there has been no mention of "infinitive mass everywhere" like the TA metal maps.
Personally, I've never experienced a fast multiplayer game match on metal maps in TA. I only ran into turtlers who had a field day playing Civ TA-style and never venturing out of their bases. Once it was apparent what they were doing, I would bid my opponent "Good day!" and just quit the match in disgust....