Monorails are stupid. You get light rail capacity for metro rail cost, and you have absolutely no flexibility.
Here's why they're dumb: Monorails are, by definition, 100% elevated. That's OK if the line you're planning is going to be 100% elevated anyway, but if you want to put any of it on the surface (you know, like
regular tracks) then too bad, you have to pay the cost of elevating it anyway.
And it doesn't connect to other modes. Build a light rail or bus subway and you can run regional routes through it. Build a monorail and you force a transfer.
And you know what's even more visually intrusive than some buses? A giant elevated structure, that's what. Somehow, I don't think that's what the people who want to get rid of buses have in mind.
There's a reason you generally only ever see monorails as recreational transit (ie Disney, Vegas, and museum shuttles). It's too inflexible a technology for real urban use.