Why are so many people advocating for the restriction of Mishra's workshop ? I find this very notion outrageous... The goal of Br policy is to regulate dominant decks and promote diversity not to eradicate a deck from the format completely.
If Workshop were to be restricted the metagame would devolve into a mostly blue cannibalistic slugfest where almost everyone is playing quad missteps and flusterstorms/ white eldrazi and dredge. I doubt it would be a lot more fun than the current two deck metagame.
I would rather advocate for the restriction of thorn or the ravager ballista combo (AND Monastery Mentor).
The reasoning behind restricting thorn is that it is much better than sphere at the moment due to being largely asymmetric given the creature focus of the current iterations of Workshops. At the moment shops are so fast that a single thorn can be enough for them to out-tempo the opponent especially since it doesn't slow down the shops player's development at all. Restricting thorn would also give combo decks more breathing room, allowing them to take metagame shares and thus increase diversity. Mentor is so good in part because it is the best win condition under thorn of amethyst and it fights workshop on their aggressive axis.
Restricting ballista and/or ravager alongside with mentor has the potential to increase diversity by making aggro control decks competitive again and diversifying the win conditions that blue decks use.
I don't think that outcome needs to be touched for now, as it is vulnerable to null rod effects and artifact destruction which means that if its metagame share starts to go up, it will be relatively easy for the metagame to adapt. And if/when it starts to dominate we can always restrict it down the road.