Feels like there are two questions here: Would it be sweet to try to see someone make Replenish work? And would Replenish actually work.
It would be sweet to see someone try this, so go for it man. I kinda doubt you'd win much, but when you did... oh boy.
My doubts are two-fold. I don't think Replenish is nearly as powerful as many other 4 drops, or even other 4 drop combo pieces (Paradoxical). So this deck, whatever it looks like, probably wouldn't power past other combo decks in a race. SO we should ask if it has other advantages, like being more resilient or consistent or something? I bet, without ever looking at it, that it would be easier to disrupt because of Dredge. I'm not saying it would lose to Dredge, but that Dredge being in the format would cause it to lose. A big advantage of being the unorthodox deck is that people probably won't know how to play against you, and they probably won't have a SB ready. But against Replenish, tons of people would likely be loaded for bear against you, because they were already prepped for Dredge and their graveyard hate will hurt you a ton. SO, though I love the card, and I think it would be awesome to see someone run it for the coolness factor, if you're asking whether it can cause winning to happen, I have my doubts. Best of luck though.
I suppose there are two possible approaches.
You can use Replenish as a combo card by building a deck that puts a kill in the yard. I remember Pandemonium+Saproling Burst, though there are probably a lot of other 2 card kills now. I suspect that this runs into the problems @Topical_Island mentioned. I wouldn't say the idea is a total nonstarter though, as I can't think of anything that combo is strictly worse than. There are a few things Replenish has going for it that other cards don't ... I don't know if those things are that important, but I've never tested it to know for sure.
You can use Replenish as a utility card in a deck that already happens to have enchantments that might end up in the graveyard ... either by being destroyed or put there (with an Entomb or a Gifts Ungiven or whatever). This approach is super interesting from a brewing perspective, but I don't know if the power level is there.
Vintage Enchantress would run Replenish, but I don't know what Vintage Enchantress is viable.
I think I'm actually most interested in the idea of a Landstill deck. There's an absolutely clear path there to getting enchantments in the yard. Replenish to get back 2x Standstill at once is actually pretty mind-boggling. You'd want to combine this with some other enchantments that do something, maybe Oath of Druids or Myth Realized, and make sure to take full advantage of good looting effects like Dack Fayden or Jace, Vryn's Prodigy. Enough of those and you could justify running (a SMALL number of) some of the top end game-ender enchantments, Form of the Dragon or .... Sandwurm Convergence??
okay I think I just talked myself into building a TERRIBLE deck.
The Leylines are also good here. Lotv and LoS are both very good already.
There are so many neat potential graveyard based decks. The problem that I run into when brewing these is that dredge is substantially better. It's like playing a burn deck full of incinerates when you could be playing a burn deck full of lightning bolts. (I keep trying anyways because I love to brew) To try to solve this, maybe there can be an instant kill combo, like hermit druid style?
This is good feedback. It does come down to building a fun deck vs a competitive deck. I was thinking of an OmniTell type deck with Yawgmoth's Bargin and Omniscience. It is essentially a combo deck with back up. I built the latest version of the Bargin and the deck is solid but I cannot see playing it a large event due to variance and counter magic.
I was hoping that Replenish may offer a way to sure up some of the weaknesses or maybe there is an old/new deck here. Something like Rector Trix but better?
City of Solitude sounds like your best friend.
@serracollector I love that card!
@serracollector You just gave me a great idea. I have been going through old cards and I could play Recycle
It may be better than Yawgmoth's Bargin in a deck that runs Replenish
On cockatrice I played around with a monogreen enchantress list for a while. It honestly wasn't half bad and won me a few games vs Tier lists, but I never got around to tuning it.
Some time ago I played around with a UWG Enchantress deck on MODO, which used Mystic Remora as one of the enchantments. I was playing this when Gush was a 4-of and it honestly worked fine too. The problem I had was that it wasn't consistent enough but I never worked on it much to get it right. There might be something along this direction for you to consider too!