Since the bigram far outweighed the monogram, there are probly trigrams (eg, N/R/S or R/S/T) with even more transposals
. In any case it seems we do need vowels for very short consonant groupings.
Most of those I report are "trivial" as defined by Corbin, in two ways: 1) expanded from shorter forms that are also transposals
, mainly by pluralising (Adding-s to gerund nouns is legitimised by Webster's Third New International Dictionary [Web3]: see "[-ing.sup.3]".); 2) having more than a short stretch in common.
Of course the well-known palindromes, charades, Tom Swifties, transposals
, lipograms (as you might not know, apart from the English translation A Void--and a Spanish, an Italian, a German, a Japanese, a Turkish and other translations [!]-there is also a Dutch translation  of the e-lipogram La Disparation by Georges Perec ), eponyms, word ladders, pangrams, word pyramids, spoonerisms, homonyms, collective nouns with a twist ("a handful of fingers", "a church of hypocrites", but the other hundred or so are not translatable that easily), chronograms, epigrams, rebuses ("M A Z T", in Dutch pronounced as "Em-a-zet-thee", meaning "Emma makes tea"), oxymorons, acronyms, acrostic verses, anagrams and alliterations.