Last year we've reworked invitations and layout in the enterprise 3.5 branch of kdepim to improve the user experience working with them. I think this is an improval over current master. We've talked to heavy users of the invitation mechanism to find what was important to them and took a look at how other MUA's handle invitations. It includes an integrated "This are your other events on that day" display etc.

The commits in the enterprise/e3 branch range from:
ee12c083fde1d7a9a66e87df7c206f4f09eec92f to 69dba4960b0f0b60c71c70a0071d78e325d6fecf

It is a pretty complicated patch set to forward port but I think it should be done.
Maybe I'll do this but If someone wants to pick this up it would be great.

Trying to get some screenshots how it looks in e35 nowadays.