@fsecco If there was a land that said "T: Add 3 blue mana to your mana pool, spend this mana only to cast blue spells", would it be restricted?
At this point in magic's history, there are enough powerful artifacts at extremely good rates (think: walking ballista, ravager, spheres, etc) that the "drawback" of only being able to play artifacts is almost irrelevant - the best artifacts in magic's history would still be good cards even if they weren't being powered out by a Black Lotus land.
Just like, even if there was that fictional 3 blue mana land (which would surely have been restricted a long time ago), blue spells would still be competitively played with lands that only generate one blue mana a turn.
If Workshop is restricted, the deck will still be powerful and functional but not oppressive, regardless of future artifact printings. The problem is really the degenerate mana ramp that Workshop provides.