There is a range of strict VST midi plugins out there - Piz Midi plugins to mention one set of a couple of dozen useful stuff for midi.
But these has to be routed like one synth to another, and does not list among midi inserts in Cubase.
If Steinberg made a VST MA(I think midi insert format for Cubase) plugin listed among midi plugins available - that take normal VST with midi in and out - what a boost. This would make manipulating midi a treat in comparison to now.
And you can also add your arpeggiators to normal midi insert part in Cubase.
As most of Piz plugin are gui-less - this wrapper need to support gui-less plugins, as most hosts for plugins do.