Thanks for your suggestions, @zwbetz! I simplified things a bit to use .Unix
rather than a prescriptive $date_format
. This does seem to be a little bit more difficult than it should have been, but alas, a solution:
{{ $futureContent := slice }}
{{ range sort (where .Site.RegularPages "Section" "events") ".Params.start" }}
{{ if ge (time .Params.start).Unix now.Unix }}
{{ $futureContent = $futureContent | append . }}
{{ end }}
{{ end }}
{{ range $futureContent }}
{{ .Render "summary" }}
{{ end }}