The idea of cloning isn't new to the Marvel universe. There was the infamous "Clone Saga" in Spider-Man comics and on the X-Men side, the time-travelling mutant known as Cable even had a clone. SHIELD experimenting with clones would be an weak plot device compared to the sheer amount of other (more interesting) lore to draw from.
Coincidence or not, Coulson stars in the Ultimate Spider-Man animated series, voiced by Clark Gregg. Still, the concept of clones is arguably obsolete and quite a bit less fitting than the Life Model Decoy.
Verdict: With Life Model Decoys on the table, cloning would be a weak and odd substitute.