Actually Planetfall has NEVER had civic maintenance.

And since inflation has been removed, this means city maintenance and maintenance reducers have less of an effect now. I can always experiment with changing city maintenance costs if this proves a problem.
What exactly is the problem of a zero-expenses economy??
AFAIK the reason Civ4 added maintenance costs was to counter ICS and REX, ie Infinite City Sleaze and Rapid Expansion.
Should ICS ever become the dominant tactic for everyone, I can simply increase number of cities maintenance costs.
Regarding Rapid Expansion... depending on your map settings in Civ there can be a shortage of land, so there's race to grab as much land as possible before everyone else, even though this hurts your economy on the dhort term. In Planetfall however, there is the entire ocean to colonize. So personally I never feel the urge to REX. There's always room left to expand to should I wish to do so.
Regarding the Hybrid civic...
The ideal I'd like to achieve is a contrast between Terraformers and Hybrids.
Terraformers would have large populated bases with high-yield terrain improvements such as farms, boreholes and condensers which cause eco-damage. Hybrids would have more bases and control a larger territory, but their bases would be smaller, and there would be less terrain improvement, relying on the +1 mineral for fungus. Unfortunately at the moment the AI is unwilling to cooperate with this.
Anyway, the point is, I *want* the Hybrid civic to lead to an ICS playstyle. To do so, the civic should give a large reduction in number of bases maintenance. So rather than reducing that maintenance reduction, I'd look towards giving the civic a penalty to make it more balanced. Perhaps a Health reduction? Fits with the goal of smaller bases.