For what it's worth, I agree that there is something here that might be Vintage worthy. If you hadn't posted this I would have written something similar my self.
Currently there are several infinite combos involving this card which use clone effects and Animate Dead to produce infinite mana and infinite opportunities to cast permanent spells from the graveyard. There are already EDH lists which are available based on infinite loops involving Muldrotha, the Gravetide. Preliminary testing appears promising in that format but EDH is not Vintage. The first questions I asked my self when I saw this card spoiled was whether it was better than the currently available graveyard recursion infinite combos that Oath grants access to. The two most famous of these engines are Black Lotus + Auriok Salvagers and Saheeli Rei + Sun Titan.
Auriok Salvagers is easier to hard cast but does less things and costs more mana if you don't already have Black Lotus; therefore, Muldrotha, the Gravetide is potentially better if you're either not worried about having enough mana against a Graffdigger's Cage or if you are up against an opponent who has managed to exile your Black Lotus. If, for example, they have used Tormod's Crypt on your graveyard while lotus is in it then Muldrotha, the Gravetide has a greater potential to allow you to recur a broader array of permanents from your graveyard once you've refilled it than you could with Auriok Salvagers. You also don't need to play white to access them. If white is the fourth colour in your Oath of Druids build then that can mean a lot.
Sun Titan is the same converted mana cost but again is white which, depending on other choices you've made in the colours of cards in your deck, can be more difficult to produce. The black tutors have a long history of being included in Oath of Druids decks so there is incentive on all sides when considering playing black as your third colour, playing a non-black third colour, or playing four colours. That is something that you'll have to decide when considering whether to play Muldrotha, the Gravetide in an Oath of Druids shell.
I have played both Eternal Witness and Snapcaster Mage in Oath of Druids prior to this card being spoiled and I firmly believe that there is a potential meta that would allow that to be a worthy consideration but I have no idea if the current vintage climate in any particular locale or MTGO would be suited to playing those cards with Oath of Druids. The fact that they're not seeing play already leads me to believe they are not worthwhile inclusions at this time. Eternal Witness plus Muldrotha, the Gravetide plus a sacrifice outlet allows for multiple ways to take infinite turns with Time Walk or Time Vault but the same was always true of Sun Titan also and as far as I know there are no competitive lists aiming to do that. That suggests to me that it may not be playable in any particular meta at this time. I would expect it to be be similarly disincentivized in an Oath of Druids deck based on Muldrotha, the Gravetide.
It seems likely to me that the best build which involves Muldrotha, the Gravetide would include an infinite mana loop involving Black Lotus, Animate Dead, and Dance of Many but would also include other value engines for situations where an opponent has managed to exile one of the combo pieces.
It is also worth noting that this card is more susceptible to removal than most of the Oath of Druids targets which currently see play. You cannot access it's ability during your upkeep in the normal case which means this card does nothing against a well timed Swords to Plowshares or Karakas activation. This downside is reduced when Muldrotha, the Gravetide is cast from hand but when Oath of Druids places Muldrotha, the Gravetide into play there is the potential for it to do literal nothing against instant speed removal. This is the single most important downside to playing Muldrotha, the Gravetide over the already establish suites of Oath of Druids targets that are currently seeing play.