How about a hybridized system of ELO and ProPoints?
Here's what I mean. ELO can be used for the Swiss rounds only, and ProPoints can be used for the Top Cut. At the end of the season, you use some combination of ELO and PP to determine the players that earn their Ratings Invite.
The main thing that I dislike about ProPoints is that it completely shuts out those that don't live in a large city where P!P is prevalent and readily available. My players have exactly two decently sized tournaments every year within 2 hours of their home League. Everything else, they have to travel for. This isn't because our area is lacking a TO willing to run more events (I'd run something every weekend if I could). It's because the area itself is smaller, and thus garners less attention than the larger cities. ProPoints-only would mean that my players would never be able to earn their invites through ratings. At least with ELO, they have half a shot given consistent high performances at the local events they participate in and the 2-3 big events (States, Regionals, and Nationals) that they can beg into. Another problem is that it's difficult to quickly verify ProPoints without multiple sources of information.
The main benefit with ProPoints is that it is purely a reward system. As such, the players that can attend and perform well at more tournaments have a better chance at getting their Points. "Performing well" in this case means Top Cut qualifications and victories, almost regardless of Swiss Round activity. It would encourage smaller events to become larger to entice a larger Top Cut, and thus more points.
The main problem with ELO as a purely reward system is that it discourages people from competing at tournaments. Not from playing, but from competing. As stated with Fulop's case, it's possible to show up late, get that R1 loss, take 2-3 quick wins from "lower" competition, and then drop to protect the rating.
The main advantage to ELO is that it's Zero-Sum. This makes it very easy to verify whether or not the information is correct. If everybody in the system averages to 1600, the system is working correctly. It also encourages players to compete at higher level events (though at the expense of lower level events).
If there is some sort of hybridized system between ProPoints and ELO that maintains the P!P standard of all events (except Worlds) being open to the public, I would jump on that in an instant. But, as an either/or type of deal, I much prefer ELO to ProPoints. I just feel that ELO provides fewer downsides than ProPoints.