You can increase the map size already, but we have no plans to support any higher map sizes as 4km² (what works above this is unsupported nontheless, but from a technical point you can go up to 16km²), as the map sizes we offer are very sufficient for any playstyle we've seen yet. The tendency of players to create maps that are too big is a 'player-issue'. It simply makes many important matters of Eco like Ecology and Property Disputes void and inexistant. If you want to play Eco as we intended it, the default size and depending on player count the sizes up to the maximum supported size of 4km² are very sufficient.
If you do not want to play the intended way you can still use up to 4km² with support or up to 16km² when you know what you do and never need support. But your experience will be vastly different and without any worries.