I think I am now able to build a Japanese dictionary for the KT from scratch. The major advantage over manipulating the original dictionary (e.g., by adding English definitions) is that one can add new entries. By this the usability would increase drastically for me. However, the way dictionary queries are handled limit the usefulness of any Japanese dictionary. The developers of the search function concentrated heavily on the Kana-version. The problem in this is that Japanese has a lot of homonyms. Two words with different meanings but same pronunciation can in almost all cases be distinguished by their different Kanji writings, however not if they a written in Kana.
I did a short test. There are for instance the Kanjis 他, 多 and 田. They can all have the pronunciation "ta" and therefore the same Kana writing. So what does the KT show if one searches for these Kanjis?
1) For 他 (meaning "other") the KT displays the entry for ほかほか, which is pronounced hokahoka and has the meaning "very hot (food)").
2) For both 多 ("many") and 田 ("rice paddy") the KT displays the entry for "た" which is sort of auxiliary.
In all three cases the wrong identification is caused by the decision to first replace the Kanji with one (of several possible) Kana-writings and search then for the Kana.