Is Baton Pass (with specific reference to full Baton Pass teams) a problem for the development of the metagame?
No. Out of all generic team archetypes, I have a MUCH easier time beating the full Baton Pass team than, say stall or Deo/Sharp HO. Though, to be fair, most of my teams have Volcarona and Scizor (mostly because I love them) and a phaser of some kind. If I can outpredict to remove the boosts (haze being the move that gives these teams the hardest time), and wear them down, they're not doing a whole lot to me. A weakened, unboosted BP team is setup fodder for my bugs. These teams usually pack 3 things that are weak to Scizor's moveset (espeon, Mr Mime, Sylveon), and one that dies to him anyway (Smeargle). Most of these teams also die pretty fast to strong special attacks with their boosts gone. Volcarona is perfect for eliminating many things on these teams, with his own boost move. Bug Buzz hits behind subs, and hits most members of these teams hard. Quiver Dance will boost special defense in addition to speed, making it more difficult for these teams to take him out.
That being said, nothing is a free win against these teams. They often get their own hax too, for example their own crits or moves like Scald/Tbolt getting burns/paralysis or my moves missing. But I still find them to be much more manageable than the other generic team archetypes on upper ladder. I do understand why people have a tough time, though. Most offensive teams do not have room for Haze, and not every team suits my favorite bugs. If an offensive team lacks a dark type and a decent wallbreaker, there isn't much stopping Stored Power from shredding through everything.
If so, what elements, in particular, do you think are pushing Baton Pass over the edge?
If anything, it's those teams that aren't full BP but still have a Scoliopede, to pass attack/speed boosts to a completely different target, such as a Mega Pinsir or a Bisharp a lot harder to deal with. With these teams, you can't necessarily predict what your opponent will think of as a possible recipient (most of these teams use 3 dangerous physical sweepers, often running additional coverage moves instead of their own boost since they have Scoliopede), and they tend to boost atk over def. If your haze user dies, or if they have a recipient that can hard counter it (such as a grass type in the case of Quagsire, or a ground type if you're running Roar on Heatran), it is a lot harder to deal with than the full BP team. But still not completely broken or worthy of a ban IMO. Like anything, it can be played around/must be considered.
Do you believe that banning individual Pokémon (such as Espeon/Scolipede) would make Baton Pass manageable?
It would make it easier to manage, that's for sure. But I don't think banning them is necessary.
Would you support a blanket ban on the move Baton Pass?
Absolutely not. Even if full BP teams weren't a thing, the move has uses that go beyond passing boosts, such as escaping Pursuit traps. With Pursuit being extremely common, it's nice to be able to use Baton Pass for the sheer utility of the move if you have a ghost or psychic type that has access to the move.
Would you support the introduction of complex bans (like Pokémon X+Pokémon Y on the same team)? Feel free to suggest more forms of complex bans, of course.
No. Partial BP teams are more difficult to deal with than the full BP team, due to being far less predictable. Neither is broken.