One that I have been thinking of is basing the
suggestions on
existing links - if you go through Wikipedia, almost all pages on
which the word 'Einstein' occurs will also have this word as a link
(or part of a link). Thus, if "Einstein" or "Albert Einstein"
occurs
on a page without links, it's likely to be a term that is useful to
link. On the other hand, the word "never" will occur unlinked on many
pages, so it is not a good word to suggest as a link either. I haven't
tried it out, but it does have the advantage of working for redlinks,
disambiguation etcetera as well.
That's sounds like a very intensive process. You would need to form a
list of all words that appear in your site along with a measure of how
often they're linked - that's a long list! And you would need to keep
it up-to-date...
Updating it probably isn't too bad, so it's mainly the effort of
forming the list in the first place, which on a large site would be a
big job.