Biased as it may be it is better than creating statistics from Steam numbers or YT surveys.
If it's biased, then it's just as useless a data source as other biased things like YT surveys.
(Active Steam user numbers are an entirely different category, as it has nothing to do with any specific question like ship interiors, it's simply a number of a random subset of players, the over-time changes of which can be used to as an approximation of the change of the total player numbers, but that's it).
Fdev presumably have access to more accurate (non public) data sources regarding actual player numbers, but accurate measurements of the distribution of player opinion on any specific topic do not really exist. Not that it's very important since nobody denies that ship interiors is one of the popular ideas. What matters is the feasibility - basically a cost-benefit analysis, taking possible technical difficulties and gameplay benefits/downsides vs the available dev resources into account.
As for potential gameplay benefits, it's mostly a matter of taste ofc, but based on the gameplay quality of previous updates (like EDO itself, for example) I absolutely don't think it would be worth it even to think about ship interiors for a split second. It could even happen to end up ruining what good gameplay we have, because of the high probability of bugs.
As for resources and technicalities, fdev are understandably silent about them (as always). What little data we have is mostly the quality and complexity of the recent updates, and those absolutely don't justify high expectations. EDO was the last big thing and it did not go really well. Fdev have only attempted smaller, 'minimally invasive' (relatively speaking) updates ever since then.