Lingua Franca come and go. They are universal in that they allow people with different mother tongues to communicate with each other. In the time of the Roman Empire and far later, Latin was such a language, though it is now a dead tongue - read (rarely, and by scholars), but not spoken. French was once a major international language (we still use par avion for airmail, a remnant of that time). The rise of British power(...) led to English becoming the new language of comminication (...)
And so on.
Pardon me? First of all if you are using lingua franca as a plural and you are an editor, then, please, it's either lingua francas or linguae francae, then, I find the discussion rather narrow. What about the role of French as lingua franca in Africa? What about literary Arabic as veicular language for the Islamic community world-wide? What about Kiswahili? Or Spanish in Latin America?
As to Latin... read (rarely, and by scholars)? I guess someone forgot to tell the guys that publish these , or this, or any of these guys (and gals). or the folk over at Vicipaedia, moreover Latin is still the official language of the Holy See, official documents are published in Latin, their web site is available in Latin and Latin is even a possible option for their automated teller machines (that are also very polite) : "Inserto scidulam quaeso ut faciundam cognoscas rationem".
Not spoken? About 15 years ago a delegation from Poland came here, we meet them in several occasions, during one lunch I listened to my dad and one of the delegation members (their parish priest) conversing amiably in Latin for the whole time with no trouble whatsoever (neither of them was a Latin scholar, they both had learned it in high school). It drove me crazy because, while I understood perfectly, I was unable to speak, the teaching method had changed by my time. BUT that isn't true everywhere, and even here more and more schools are going back to Latin as a 'normal' language for instance using Lingua latina per se Illustrata or other similar books as textbooks.
Then there's Nuntii Latini , a regular news broadcast on Finnish radio, Latin circles everywhere in the world and even instances of multilingual families where Latin is used as the everyday in-home language so that neither of the parents' native languages would dominate the other. Do they speak like Cicero? Definitely not, but, you know, when at home even Cicero did not speak like Cicero .
In short, Latin speakers may not be as many as English speakers, but Latin is alive and well, thank you.