Gebser is, I would say, a Dichter (which is most often translated into English as “poet”) but it is used to identify anyone who works well with words. Hegel, Heidegger, Nietzsche, and other philosophers were referred to by that term, as was Goether, even when he was writing science and not literature. Thomas Mann, known for his prose, is also considered a Dichter. Yes, Gebser was also a poet in the sense that he wrote poetry.
And there’s another little linguistic twist I’d like to mention. The German word for “science” is Wissenschaft, and this term can, and is, applied to any area of serious investigation and study. So we have Literaturwissenschaft (lit. “literature science”), Sozialwissenschaften (lit. "social sciences), Ingenieurwissenschaften (lit. "engineering sciences), and so on. So when you say “Wilber is focused on science”, I understand that he’s focused on the natural sciences. In English, the term has taken on a very focused meaning that is not shared everywhere. We in English, and this is part of Kripal’s case, separate the sciences from the humanities; but in German there are the Naturwissenschaften and Geisteswissenschaften (and the word Geist in there probably means “mind” as well as “spirit” as well as “soul”, which are all common translations of the word). Whatever struggle there is between them is qualitatively different here than in North America where there is a movement to have them eliminated, as far as possible. (Of course given the nefarious spread of neoliberal ideology and a continuing Americanization of much of European culture, I am not maintaining that it will stay that way.)
One of Gebser’s most admirable accomplishments was that he had a flash of insight that he developed and explicated almost exclusively from within the mainstream. When you look at the sources he uses to document his opus, they are not marginal at all. He was certainly sensitive to the margins, but bringing them in to substantiate his case would have been risky. He’s ignored more than rejected, I believe, because he played the game well in making his case, and if he’s correct in his assessments, a whole lot of rethinking needs to be done. And I think we all know how that is going to play out.
Barfield’s primary possible contribution, Saving the Appearances, didn’t appear till 1957. I think it is clear that Gebser wouldn’t include Steiner in his work, as Steiner is perhaps the most well known of the “traditionalists” (in contrast to the “evolutionists”) from whom Gebser made great efforts to distance himself. And let’s face it: it is only most recently that a scholar like Gidley could even make a serious statement of any kind mentioning Steiner, Wilber and Gebser. I’m not sure that would have even been possible 10 years prior.
Having said all this, though, I agree … at some point I’m sure that we’ll invite both Steiner and Barfield to the table. And I, for one, am looking forward to it.