I vote for options 3 and 4.
I recently ran into this problem with Naruto Shippuuden: Ultimate Ninja Storm 2. Sure, there are only 2 online multiplayer trophies, one of which is simply winning a single match, but at this point, people still playing the game are few and far between, and from what I saw, most of them are pretty high-level players (or just cheap), which makes it very difficult to win even just one match, nevermind the ten required for the other trophy.
My main problem with online multiplayer trophies is precisely this: when the fanbase dies out, so do your chances of obtaining these trophies if you didn't get them while more people were playing. And that's just bull, IMO. Sure, from some business perspective, I'm sure it makes plenty of sense, giving more incentive to purchase the game at launch and whatnot, but it just seems like such a dick move, screwing over late players who want to get that platinum/100%.
But then there's also the problem of tiers, leaderboards, etc. I don't think many people out there are willing to sacrifice their precious e-peen just to let others pick up these trophies, so if you can't manage to get matched with anyone around your skill level, you're forced to either pursue some hardcore training regimen to shape you up for the elites, or just give up on ever getting the trophies. And this problem, as mentioned above, becomes ever greater when the number of players online starts to thin out.
Granted, much of my dislike for multiplayer trophies is biased due to personal problems with them... ^^; But really, I don't think there's anything wrong with them, regardless of difficulty. They're additional challenges, just like any other trophies. The problem, IMO, is how they're included in the pursuit of platinum trophies. I think the simplest and most fair way to do multiplayer trophies would be to just give them in a bundle like DLC trophies, which wouldn't affect attainment of the platinum trophy, but would still provide the extra challenge for those who want to pursue them, and would crank up their completion percentage beyond that of those who opt out, giving additional bragging rights. And considering how the multiplayer modes for most games seem to be almost completely separate from the main game (if not literally completely separate), the platinum would still serve to represent 100% completion of the main game's challenges, while the extra trophies would build up to 100% completion of the entire game's challenges.