For myself, I have the idea that slightly Southern cities may be more conducive to wandering around without rain, in the Spring time.
Did Rome ever get picked?
How about Prague? (As well as being very interesting and historic, it is very close to Hradec-Kralove and the Foma factory. Possible climate problem
😉).
Is Beirut too far away? (Depending on local political conditions, next Spring).
Lisbon interesting for us maybe?
Then there might be Ciudadela? (Old city and with a multi-national history, and sun & people).
Zagreb or Split? (A bit less sensitive, but still interesting in F.R.Y.)
Marseille? (Huge and alive, but maybe people want a different country, having visited Paris).
Trieste, Slovenian coast might be interesting?
Arles - the first week of June is a bit late perhaps, but that is the opening week of the
Rencontres d'Arles.
And I'll be going back to Istanbul too, but two consecutive RFF visits for the city might be too much and they won't let us in . . .