Lyric elision using slur marks, between notes, not for a single note
There should be a simple way to show elision between words in lyrics. The simplest way to do this would be able to add a slur mark to a lyric syllable after the lyrics have been entered, just as can be done with notes. The slur mark could potentially occur at the end of a system, connecting to a lyric on the next system. Similar constraints as for notes would apply as well. There would have to be a note following (not a rest) in the same voice part with a lyric entered in the same verse as the lyric where the elision mark originates. For typesetting, the slur mark would anchor at the end of the first lyric syllable and the start of the next lyric syllable. There is no need (indeed it would look silly) to be able to flip the direction of the slur mark.
This is most useful when adding lyrics in French, where elisions are common, but don't happen all the time, based on context, punctuation, etc.