The way I think works.. is transaction happens in Fiat at the POS... XAPO just takes the exact amount plus a fee from your bitcoin bag.
The Bitcoins only travel between XAPO and the Bitcoiner. Not through the Merchant.. I believe and correct me if I am wrong.
So this is not a solution at all. For Bitcoin to spread its wings, the coins need to flow through The Merchant, The POS AND The bitcoiner or bitcoiner-ette.
In Xapo's case, the merchant never sees the coins.. so what is the point?
The point is you get to spend your at a place where they won't normally take btc. Most businesses aren't going to accept Bitcoins based on the fact that it's new, unregulated and the creator is unknown.