A friend of mine explained me a bit of how this theatre things works, and looks there is something we didn't considered yet.
Competition.
I guess that would be something in the West End things but, theaters are pretty close one from another, and they have to compete with the others and what they have on their schedule, so quite often, theaters would announce their plays or schedule them in competition with the rest of theaters, sometime to confront, sometime to avoid that confrontation...
That might be the reason why Local Hero wasn't announced yet. When it was at the Old Vic that wasn't a big issue as that theatre is not in the West End but close to Waterloo station, and it is an independent and charity theatre, but if the musical is going to other theatre that it's on the West End circuit, or have competition close, they might be holding the announcement for the right moment.
Quite an interesting world.