We could force an upgrade to the latest version, like it was done for emacs22 and emacs23. I don't know how an init file written for emacs-21 would behave when interpreted by emacs-26; expect some bumps. On the other hand, people who want to keep emacs21 can still look in the Attic.
Diff below. I needed to explicitely list the no_x11 flavor as below in order to hint pkg_add -u, maybe this should have been done for emacs22 and emacs23 too. Input welcome, Index: Makefile =================================================================== RCS file: /d/cvs/ports/editors/emacs/Makefile,v retrieving revision 1.78 diff -u -p -r1.78 Makefile --- Makefile 4 Sep 2018 12:46:11 -0000 1.78 +++ Makefile 31 Oct 2018 00:28:03 -0000 @@ -4,7 +4,7 @@ COMMENT= GNU editor: extensible, custom VERSION= 26.1 DISTNAME= emacs-${VERSION} -REVISION= 2 +REVISION= 3 CATEGORIES= editors Index: pkg/PLIST =================================================================== RCS file: /d/cvs/ports/editors/emacs/pkg/PLIST,v retrieving revision 1.22 diff -u -p -r1.22 PLIST --- pkg/PLIST 4 Sep 2018 12:46:11 -0000 1.22 +++ pkg/PLIST 31 Oct 2018 00:28:03 -0000 @@ -1,5 +1,9 @@ @comment $OpenBSD: PLIST,v 1.22 2018/09/04 12:46:11 espie Exp $ @option is-branch +@pkgpath editors/emacs21,-main +@pkgpath editors/emacs21,no_x11,-main +@pkgpath editors/emacs21,-el +@pkgpath editors/emacs21,-leim @pkgpath editors/emacs22,-main @pkgpath editors/emacs22,-el @pkgpath editors/emacs23,-main -- jca | PGP : 0x1524E7EE / 5135 92C1 AD36 5293 2BDF DDCC 0DFA 74AE 1524 E7EE