I'm not a fan of having to pay a yearly fee to play a game online (like I did for TW on Xbox 360 for a few years). The majority of PC games are free to play online unlike the consoles (which is fair IMO considering how much more expensive PCs are). I definitely think free online play should continue with the next version of PG.
Microtransaction items like PP courses and balls could continue to be sold and new items like extra golfers, carts, clothing, equipment, etc could be added to the list. These would all be optional of course and the extra golfers/equipment wouldn't give the player any advantage over someone with the basic equipment/golfers (it would just be for show). Many games nowadays use this kind of microtransaction model and I think it's something PP should definitely continue for added revenue.
Perfect Parallel could also consider placing ads in the game for additional revenue. EA did something like this with a number of TW PC games, adding an ESPN sports ticker and ESPN radio updates in the multiplayer lobbies. I wouldn't want to see much of this during an actual match though, with the exception of maybe signage placed around a tee box much like you see for sponsors during most professional golf tournaments.













