We would have little hope understanding the language of the future as so much of what we write and speak is predicated on new technology and the adoption of jargon that is deliberately non-inclusive.
Consider what a time traveller from a hundred years ago - even forty years ago - would have made of expressions like 'click your mouse', 'depends on how much ram you've got' or 'do a web search'. Perhaps they would be reassured that we still had a strong connection to animals (a different thing to animism. Thank the all pervading spirit for edit function).
"Prithee fair maiden" features low on the list of chat up lines (I don't know this for a fact but it's a fairly safe bet). Who knows how it would have been received when freshly minted. Language, especially the flowery and overblown kind, can become gauche; grating on our nerves, it wears out its welcome.
And "Gadzooks!" has probably passed being used for comic relief; a sure sign of being archaic.
I don't think, even now, that experts can agree on which words we should fight to preserve, which vulgarisms we should struggle to avoid. Do we permit the portmanteu, accept the acronym, approve the abbreviation? Do we have a choice? We can always bide our time and hope that, say, wicked will return to its wicked ways or that sick will spike a temp
Citizen 2040 won't necessarily have a richer vocabulary. The lingua franca will shrink and grow, meanings will become clearer at times and more muddied at others. Idiomatic expressions will give the denizens of newly created borders the same kind of problems in translation as in the past.