The potential of what could happen with Spike later, as he evolves more with his powers and such, could be very intriguing as time goes on, especially if it ties into a certain S8 episode later on.
Now as far as this ep. teasing Sparity again, IMO they reason do this on occasions, is because they know Sparity (Rarity x Spike) is basically canon in the franchise, and amongst a majority of the Brony and Pegasister community. Also from what a vast majority of folks have said in the past and by proof with this episode, the Sparity focused/related episodes do some really business by the mostly positive reviews and reactions thy get.
And with that said, it further proves and adds fuel to my point, that whenever they decided to choose a time to do a final series, that they (the creative staff) will find a way to make Sparity (Spike and Rarity) Official and Visually (On-Screen, in continuity) Canon.