I didn't realise that smatview submissions were treated as slices? Thought it was only data loads (haven't spent a lot of time with users submitting directly into ASO via smartview). I suppose that makes sense though - otherwise smartview load performance would be horrific.
And for the pitfalls - fundamentally query performance will start to suffer as you have more slices sitting between the baseline data and the query. I'm not sure anybody would be able to quantify exactly what it will look like in your specific case - would seem to heavily depend on the data intersections that were loaded and the associated optimisations (and aggregate views) that already existed on the system.
You do seem to have the option of using the SELECTIVE option - could potentially tweak that have it occur less frequently?
SELECTIVE—Specifies to activate the incremental data slice auto-merge process when the number of incremental data slices specified in the AUTOMERGEMAXSLICENUMBER configuration setting is exceeded. If the number of incremental data slices in the data load does not exceed the value of AUTOMERGEMAXSLICENUMBER, the auto-merge process is not activated.
Default is 4 - maybe try upscaling that to 10 - 20 - 30 and running some test cases over it. Would definitely make an interesting case study - can't seem to find anyone writing much about it.