I would love a Klanghelm collaboration, which would answer requst for an RMS meter. Having SSDR, with a flyout to it's full VST would be cool.
I think a transient designer would be cool too, maybe extend that XLN connection.

The 6 modules of RC20, could be 6 individual PC Modules, in the same way the VKFX comes as a full VST, but is broken down into PC parts.
P&M stuff looks like would fit easy too, above in the XLN pic and here.
I know it's down to the manufacturers, but it makes the PC format so much more appealing and sonar with it. To have these to choose from would cover masses of ground.
http://www.plugandmix.com/products/software