One last SQLCLR feature I'd forgotton about but was quite highly publicized. This is extension of SQLCLR UDT and UDAgg maximum size from 8000 bytes to 2gb. You just the MaxByteSize of -1 in the appropriate attribute, like this:
[SqlUserDefinedAggregate(Format.UserDefined, MaxByteSize=-1,IsNullIfEmpty=true)]
The serialization format is going to have to be UserDefined, the limt for Format.Native is still 8000 bytes.
Just catalog the UDT or UDAgg and use it as you would any other TYPE/AGGREGATE. I crufted up a proof-of-concept one pretty easily, and the new spatial data types (GEOGRAPHY and GEOMETRY) are also large (system) UDTs, so you know this works as of CTP5.
Now you can have your "infinite" UDT that holds an array or "infinite" string concatenation UDAgg. Enjoy.