Select[Table[RandomSMW[2,4],{25000}],InterestingRuleQ]
{{BBBAAAB,AABB},{ABBA,BBABAAB},{ABA,BABA},{ABABAAB,BBAAB},{BAB,AABAB},{ABBAB,BBAAB},{BBAABB,ABBAA},{ABBA,BAB},{BBAB,AABBB},{BABAB,BBBAA},{ABAB,BBAA},{BAABBB,BBA},{BAA,ABAB},{AAABB,BABA},{ABAB,BAA},{BBAABA,AABAB},{ABB,BAABA},{BAAB,ABBBA},{AAAAABB,ABAAA},{BAAAAB,ABBA},{AAABBA,BAAABA},{ABAB,BAA},{BAA,ABAB},{ABBABB,BBAA},{BAAAABA,AABABA},{ABAAB,BAAB},{AAB,BBAAAB},{BBBBA,AAAAB},{ABBBBAA,BAABB},{BABAB,ABBA},{BBAA,ABAB},{AABBBAA,BAABB},{AAABA,BAAAB},{AAABB,ABABAA},{ABB,BABA},{BABAA,AAABBA},{AABBAB,BBA},{ABBAB,BBAA},{AAB,BBAAAB},{BBABB,ABBA},{ABAAA,AAB},{ABAA,AAAABBB},{BBAABAAA,BABBBA},{AAAB,ABBBABA},{AAABB,ABABA},{BAAB,AABBA},{ABA,BAAB},{BABAB,BBBAA},{AAABBA,ABA},{BBBAAB,ABA},{BAB,AABABA},{BABA,ABA},{BABABB,ABBAA},{BBABAB,ABAABB},{BABA,ABA},{BBAB,AABBBB},{BAABB,AAAABAA},{BABA,AAABBA},{BABAB,ABBA},{BAAAAB,AABBAA},{ABBBA,BBAAA},{BAABBB,BBA},{BAAB,ABA},{BABAB,ABBAB},{BBABAB,ABBABB}}
MapIndexed[ListPlot[StringLength/@SMWEvolveList[#,"ABAAB",40],PlotJoined->True,PlotLabel->BigFont[#2]]&,%];
(Ran 25000 search for 1 rule, size 6; nothing "interesting" found)