I'm certainly in favour.
Yes, the ethos is to base forums around FF programmes. But those forums are full of posts that have little to do with the respective programmes. Those posts are allowed and good thing too.
If Easyjet/Ryanair interest generates enough traffic to warrant their own forums then go for it. To refuse this because of a lack of FF programme seems unnecessarily dogmatic to me.
Afterall - if a lack of a FF programme is reason to exclude them from their own forums, then why should discussion of them be allowed in Budget Travel? Indeed why have any forum that is not based around FF programmes?
In conclusion - once we've overcome the hurdle of "is it a valid topic of discussion on FT?" then it should be traffic/interest that determines whether an individual forum is created.
Sure, keep discussion in Budget Travel if there is insufficient interest, but not as a "punishment" for not having a FF programme.
judolphin sums things up very well IMHO.