It's obvious, if you play all types of games under all types of conditions (practice vs play), sometimes a ball return is ideal, and sometimes a drop pocket is ideal.
So why don't table manufacturers do the obvious: Make ball return tables with simple "pocket blocks" that you could remove to use the ball return, and insert to use the table as a drop pocket. You could even have SPECIFIC POCKETS set up to do one or the other.
As a matter of fact, it would probably be easy enough to make special "pocket bottoms" that could be put into or taken out of ball return tables (with a special tool, or something, from the pocket opening), so that you could switch back and forth between both systems.
Edit: Or, I suppose you could just stick a towel down the pockets of a ball return table and temporarily turn it into a drop pocket. The last table I had was an ancient Brunswick that was built as a ball-return, but I simply put drop pockets in it instead of taking the time to set up the ball return system.