I will be curious to hear your experience. I DIY'd a version of the 5.0 / 75L. I don't think you could sup foil it, but bet it would work ok as a prone surf foil.

I was just watching the mackite review of the Ride Engine Moon Buddy 5.0 wingboard. He talks about smaller people using it as a sup, and notes it includes a front fit box for tracking. That's interesting, as I've seen Kalama boards have these for years, but first other brand offering this. Apparently only on the 5.0.

He also talks about people using their 6.0 and 7.0 Moon Buddies as dual wing/sup boards. So that may be something to do some googling on, their results for the 5.0 and 6.0 may transfer somewhat to you question on the 5.4

Will be tricky with the tracks so far back. To center your weight for paddling you'll have to be perhaps too far forward of the mast to get up on foil, doable but will require some fancy footwork.