"A Spellchecker Used to Be a Major Feat of Software Engineering"

It still is. The spell checker on my Android phone is a PIA. It's too dumb to correct many typos, there's no way of highlighting wrongly used but correct words such a 'fro' and 'for', etc. There's no automatic or user defined substitution such as correcting 'rhe' with 'the' and yet keep the words highlighted until a final revision.

Wordpossessor spellers have no way of tagging certain words that one may or may not wish to use depending on context. A classic example that's caught me out past the draft and found its way into the final document without me noticing it is 'pubic' for 'public'. Why doesn't my speller highlight such words in red and ask whether I actually meant to use this word?

Moreover, spellers are not all of the same level of accuracy, for example Microsoft Word's speller is much better than LibrOffice's much to my annoyance as LibreOffice is my main (preferred) WP.

Nor is there a method of collecting misspelled words or typos and tagging them as spelling errors or typos for the purpose of helping one's spelling or typing. It'd be nice to have a list of my misspelled words together with their correct spelling, that way I could become a better speller. Also, spellers could be integrated with full dictionaries—highlight the word and press F1 for its meaning, etc.

There are no dictionary formats that are both universal and smart, that is that would allow for easy amalgamation between dictionaries and yet could contain user defined words and other user metadata which would be distinguished from the general corpus of words when crossed or amalgamated. For example, a smart dictionary format could contain metadata that would allow a dictionary and thesaurus to coexist in the same word list, similarly so different dictionaries, technical, medical etc.

All up, spellercheckers are still a damn mess. They need urgent attention.