I asked the asp.net team directly and this was their response
We officially announced that partial trust is no longer a trust boundary for the purposes of application isolation last year (http://support.microsoft.com/kb/2698981) and as such our recommendation to shared hosting providers is to not use it anymore. Moving forward, we will not be supporting partial trust for new framework features we develop for this reason.
I know lots of people using shared hosting and since host providers won't ever give full trust to their shared hosting products I am guessing Microsoft made this decision so they can get more clients on Azure.
Puts us small developers who have clients sold on shared hosting in a predicament. Either go to more expensive hosting or jump to azure.