Freeview is a commercial operation, which charges broadcasters for access to the transmitters. Television companies (with the obvious exception of the BBC) hope to offset those costs, and to make a profit, by selling advertising. If a channel doesn't get enough advertising revenue to meet the costs of accessing the transmitters (together with the payments they have to make to secure the broadcasting rights to programmes) it won't last for long on the Freeview platform.
Many advertisers are now switching from TV commercials to other ways of advertising (such as the internet). That, together with the current economic climate, means that all commercial stations are struggling to pay their bills. (The whole of the ITV network is dangerously close to 'going under'). So there are likely to be fewer commercial channels, rather than more, across all platforms (Freeview, satellite, cable and internet).
Film4 used to be unavailable on Freeview. That was partly because of a contractual commitment to Sky but also because they deemed that they wouldn't get enough additional advertising to offset the costs of broadcasting on the terrestrial system. The company decided to 'bite the bullet' and to see what happened if they 'gave it a go'. They then decided to add Film+1 to the trial. It seems that there's enough advertising money to fund Film4 on Freeview, but not Film4+1 as well.
I doubt that Film4+1 will return to Freeview in the near future. It's far more likely that several channels (possibly including Film4) will disappear from Freeview.
Chris