1. Suppose it's better «autocomplete» word not from document itself but from dictionaries (at least have an option), that for programming language can be easily made, and for usual languages can be converted from Xspell dictionaries used in OpenOffice. With small or middle sized dictionaries in programmin langs suppose program can be quicker.
2. For the Sort Plugin may be add options remove duplicates (or calculate quantity of duplicate). Further enhancement of this plugin - creation of wordlists. (Wordlist can be obtained with macro extract by regex). For now I don't know program that can create wordlist from unicode text with characters from multiple 1-byte encodings.
3. Regarding Spellcheck - There can be easily made offline spellcheck. Button Spellcheck - check the documents against abovementioned dictionaries and highlight (or export in standalone file) words that are nor in dictionary. You check the file of not-in-dictionary words adding with tab corrected word and use another one button correct that will read both wrong and corrected word from file and correct source file with Find/Replace.
List of correct word can be used to add to dictionary.
Just one thing - there can be opportunity to add some dictionaries not one.