I've done it naively with a mongo driver. Just wrapping it in a future doesn't cut it, as you said you have to configure a separate execution context and even that context is finite. Or use a blocking future which has other implications.
It's more a point against the "strictly better than Java, use the bits you want as you you go" point in the article. You have to understand Scala's execution model and make sure you are mixing the paradigms properly, because it's fully of leaky abstractions.
Maybe I'm missing your point but as a professional Scala programmer I've never run into a problem with Jvm or Java integration