Free multiplayer people are talking about. Best prepare for the worst experience. The costs are way too prohibitive for that.
A tiered system might work, but I doubt the lowest multiplayer only tier would be as low as people would think/want it to be.
Other than that I'm actually relatively happy with PSPlus as is. Wouldn't mind a mid tier with just multiplayer, cloud storage, and share play. Premium tier(s) should be reserved for free games per month and/or streaming.