Suppose that 4 or 5 centuries from now, all sorts of scientists (geologists, paleantologists, astronomers, etc.) "find" means of explaining the basic phenomenon they each deal with in such a way that actually makes a literal-6-day creation seem very viable and even probable.
What are the possible ways of understanding such a future?
(1) All these future scientists and their popular opinions could be wrong. Maybe our contemporary scientists are generally right, and all these hypothetical 5-centuries-from-now-scientists have it wrong. That would mean that 5 centuries from now, Christians ought to argue that "day" refers to a long period of time. However, they would actually be arguing *against* their own popular scientific community of the day who would actually be saying something that appears more in line with the most prima facie reading of the Christians' own text. Should the Christians of that hypothetical era attempt to fight science with science and go out and conduct experiments of their own to prove those eons of time occurred?
(2) Maybe all our current scientists could be wrong, and all the future ones could be right. If that's the case, then Christians living *now* ought to be arguing that "day" in Genesis 1 means a literal 24-hour span of time, which is, of course, against the grain of current, popular scientific opinion, but will be supported by the trend of popular, scientific opinion 5 centuries from now. But now should Christians go out and perform "counter-experiments" and fight science with science in order to prove these eons of time did not occur?
(3) Maybe scientists both contemporary and 5-centuries-from-now could all be wrong. In that case, what should Christians be telling people about Genesis 1 both now and then? Will they be stuck and unable to explain to anyone what Genesis 1 means unless they can accompany such teaching with scientific material? Would they just have to wait around for scientific opinion to eventually come along and tell them what Genesis 1 means? If they did have some other means of accurately understanding Genesis 1, notice their teaching would contradict popular scientific opinion both now and in the future.
Popular scientific opinions and explanations could easily change every few generations. I bring that up to illustrate that with this approach, Christianity simply becomes reactive to modern popular opinion. To me, that seems to be making God's word subordinate to man's endeavors. So what is important is not what man's own endeavors tell me God's word can or can't mean, but rather, how God's word presents Itself. Through history, popular scientific opinion has changed, and i believe it will continue to do so into the future. But what has not changed in all these years is the text of Genesis 1. Whatever God meant to communicate to us when He used the word "day," He has meant that same thing throughout all these years. And it has meant whatever God intended it to mean regardless of changing scientific opinions.