CarrierWave appears to support Rails 4; the rest are not doing anything special other than making jquery js acripts available in the asset pipline without manua

CarrierWave appears to support Rails 4; the rest are not doing anything special other than making jquery js acripts available in the asset pipline without manually installing them, so shouldn't cause any issues. You'll have a bit of work to do to migrate to strong parameters, but you can always add the protected_attributes gem back to re-enable support for attr_accessible. I'd suggest checking out the Rails 4 migration RailsCast.