The issue I keep running into when testing the RCs with larger apps is the number of gems that have strict dependencies on older versions of activesupport, etc.
I am wading through my Gemfile (over 200 gems counting direct and indirect dependencies) at the moment trying to give the RC a shot, but it's going to be difficult to justify spending much more time on it, unfortunately.
Why not post your whole gemfile as a gist? People in the HN community could definitely go through and start to check some of the dependencies for you :)
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.
schema_plus (https://github.com/lomba/schema_plus) is having issues with ActiveRecord changes (API changes, methods not existing any more that they remove/overwrite etc).
I had a look at it and got through a bit of re-working some of the changes (indexes etc), but got pretty quickly out of my depth of understanding around the inner workings of ActiveRecord.
I am wading through my Gemfile (over 200 gems counting direct and indirect dependencies) at the moment trying to give the RC a shot, but it's going to be difficult to justify spending much more time on it, unfortunately.