What features are you using postgres_ext for? A lot of the ActiveRecord datatypes support is handled by Rails 4.0 (arrays, uuid, ranges, inet/cidr and macaddr are in Rails 4.0). I want to submit some pull requests to Arel to add support for some of the datatype operators
In the case of postgres_ext you should actually check to make sure the functionality you need isn't already in Rails 4. Dan McClain extracted much of what he did and got it pulled in.
I'm currently fighting with redis-rails in particular, as bundler doesn't seem to be seeing the dependency change in a nested gem.