Given that you're adding eccentric orbits to the next release, with variable colony cost being an effect due to temperature swings, what if Hydrosphere had a reductive effect on the range of temperatures a planet can produce?
As I recall, Earth's oceans actually do this to an extent both on a daily and seasonal basis. Perhaps liquid hydrospheres could start shrinking the temperature band at 30 or even 50 percent, with max possible effect at 100. Granted, if eccentric enough, even an ocean world might boil away in summer and freeze solid in winter. With your changes to water vapor there still could be borderline worlds where they are too eccentric for 0 infrastructure but not so much that 93 percent hydro couldn't counter it.
As an aside, perhaps a new facility and tech line? Oceanic Infrastructure Factories and their production rate? Built with TN due to its benefits but otherwise just a population and wealth sink to increase the max pop for a world with high hydro extent back to normal. Perhaps could be the first tech line of the prophesied pop density increases? Say once you've countered hydro completely through tech or close to it, you get a new tech that can increase max pop on worlds with sufficient hydro and excess Oceanic Infrastructure Factories. I suggest factories over just a new kind of infrastructure because salt water hates everything, so rather than one and done like infrastructure on a rock, the Oceanic kind will require constant maintenance, and the techs represent improvements in the abilities and processes of the work.
