First I'd like to say that The Events Calendar is the best of all the similiar plugins out there. I've tried so many that in one or more ways did not fit my needs and then I tried this. Great!
However - there's always a but eh - beside the features you already plan to integrate some day I'd like to see:
Meta field for participation/event registration deadline. Since you already have fields for addresses and pricing I don't really understand why this field isn't available.
Simple date picker. I know there are tons of jquery scripts out there to do this, so I don't think adding this will be hard at all :)
A more compact admin interface/metabox. It's fine as it is now, but still too big and too much unused space.
And lastly. This one can wait until the release of WP3, since it by then will be much easier to code.
Own admin navigation block. Other calendar plugins already have it. Calender Press the best in my opinion. But with the release of WP3, adding custom post types will be really easy.
That's all - for now :)