English Translation
He is now either in Rome or in Paris.
This says he is now, not “he will be” in Rome or Paris.
I think both sentences are expressing some level of uncertainty about the current whereabouts of the person in question. The words and sentences are structured differently, but the meaning is the same.
He’ll be in Rome or Paris. [That’s as much as I know]
He’s now in Rome or Paris. [Which I couldn’t say]
It is a typical case of futuro de conjetura, which is used to express supposition or assumption, but not the future tense.
- Estará en casa. = He must be home.
In both English and Spanish the future tense can be used to express speculation or deduction in the present (futuro de conjetura).
-¿Quién es ese tipo? —Who’s that guy?
→ Será el encargado — It’ll be the manager[Sounds more sure]
→→ Tiene que ser el encargado — It has to be the manager
→→→ Debe de ser el encargado — It must be the manager [Sounds slightly more speculative]
You can learn more at Futuro de conjetura - especulación