I'm analyzing a future integration into a EPiServer web site that is currently running on 3.5, 6 R1 and Relate+ 2.0. The other system will have libraries that are built targeting 4.5. There are som big advantages integrating by referencing the libraries directly into the web site project.
I haven't done any testing but I know .NET 4.5 is an "in-place upgrade" of .NET 4.0 and getting a 4.5 targeted library to run in a 4.0 web site could most likely be worked out. But having everything in the solution target 4.5 is most likely better and safer.
I know that the official requirement regarding .NET Framework is 4.0 for EPi 7. But is this so just because it couldn't be tested fully (time factors) or is there something blocking it more directly from working/running?
Also, will the next wave of EPi product versions require 4.5?
.NET Framework 4.5 should already be supported in EPiServer 7, it is the flavor of .NET 4 that Windows Server 2012 and Windows 8 come with and these operating systems are supported.
I believe the system requirements should really say ".NET Framework 4.0 or 4.5" or something to that regard. (We are not making use of anything that is 4.5 specific but it has been tested with 4.5 as well as 4.0.)