i think 2. is the most realistic case at the moment.
for 1. and 4. there are already better apps.
3. and 5. needs a lot of more horsepower then a ipad have.
the most important parts for me are stabilty and a touch optimized gui.
meteor for example, drives me nuts with the touch inoperability of the loop adjuster.
to say it even simpler “power is nothing without control”
people ask for a sampler or other instruments. ok. but look at beatmaker2 or meteor (in app p) its looking great for the feature list, but they sounding crapy.
rather I go with 24 bit or a drum editor, this will rise the level of user comfort.
point 2 of your list is mostly my “use case”.
Jan