This doesn’t directly address your request for a live(ish) feed of data but to give you some sense of where Monzo are on this, here’s what they said about importing historic transaction data -
I expect a live feed would largely be dependent on the other banks / providers, having an API which Monzo could use to access their transaction data or Monzo setting up screen scraping of user’s bank accounts (obviously the latter isn’t ideal). I expect that the APIs will only become widely available after the Open Banking standard / PSD2 regulations are applied.