Maybe i am wrong but it looks like we are not talking about the same thing : you are talking about influence of shop restriction in the actual meta whereas i am talking about influence of shop restriction in an hypothetical and mostly unknown meta related to a set of rules for B&R (opening post).
I have witnessed enough shops match ups to know that they often have superfluous mana and have plenty of games where they win on sol lands. Shops already did not come up as frequently as that deck wanted and it still dominated for years. The decks most critical drops have always been and are still are 0 and 2 drops, nothing changes there either.
When you witnessed shop matchup, did you see mulligan choices ? Because it is what is at stake here (later in the game you are right : shop has lot of useless mana). Most of the time, an opening hand with one ancient tomb and lock pieces is a mulligan. Of course, it depends on what you know about your opponent and the other cards in hands but most of the time it is the good choice.
I don't know if you ever played shop but if you did you must know that match up where opponent is running wastelands are very different to ones where he is not. There is a reason for that.
But to answer more directly to what you said (if i understood it well) : of course 1 workshop decks can be played (Legacy MUD decks do exist afterall). My point is not here, what i say is that something similar to nowadays shop builds would not be the best option for a shop deck.
I don't see why you need to throw the baby out with the bath water and redesign the deck from the ground up. We know through heuristics and our observational knowledge that the deck not only still works but is also still competent at doing what it does. We also know that the decks largest predator right now is not mana but rather a free green spell that does not care about your mana.
How good the deck is in the meta has not actually been about the card workshop for some time, it's about the hate that is played and if it can get in under that in the first place. Shops is not good because of 3 mana, it is good because you do not take damage/lose a card/etc to use it. If eldrazi were to become the better of the deck it is almost undoubtably because of other factors.
I agree with what you said but you should go further down that road. The real question is about which deck is stronger ?
- Deck 1 : is running 40 artifacts and made some little adjustements to take in account there is only 1 shop. Basically, the usual shop deck.
- Deck 2 : is running (let's say) 25 artifacts and 15 [add here what you prefer : Eldrazi / blue spoilers / one or several colors / whatever].
My point is that both decks can be played and would be competitive but the deck 1 would be suboptimal compared to deck 2. Reasons are simple : less artifacts mean less relying on singleton workshop, and also means that the nasty free green card will be less devastating. Basically, deck 2 is less sensitive to artifact hate and could potentially have access to blue power, cantrips, draw effects, ... (whatever) , in short strong new effects.
If we want to classify starting by strongest : nowadays mono brown 4 workshops decks > Deck 2 (singleton shop) > Deck 1 (singleton shop).
4 Workshop is the only reason that shop decks are playing that many artifacts, that is just statistic reasons. That is exactly why i would start from scratch to design Deck 2. The only exception would Eldrazi-Deck 2 that would be quite similar to what we have now, but any other would require a very different balance.