The Twin Otter is my favourite low altitude aircraft when I want to enjoy the scenery on short hops. This forum's post stats indicate the Twin Otter is second only the the Airbus variations in the Aerosoft stable so that should say something. It seems the 400 glass cockpit is unlikely so something that would work with Navigraph in the 300 would undoubtedly be well received. There is a wealth of wish list items here and elsewhere for the Twin O.
I would part with around 15 Euros for an upgrade that gives me flight plan capability and addresses the tweaks/issues that have been mentioned along with DL- it would make a great aircraft even better. Largely I believe because a simmer can put it down at any alternate and its fun to fly, and that allows most simmers not only to enjoy a great aircraft but also to hop around all the great airports that we have in our simms especially v4
Good luck with the redevelopment of Extended Mk2 we will wait patiently.