ext4 has some support through the older ext2* projects. btrfs has no current Windows support. New filesystems are always going to have a period where there's no support on another operating system and, frankly, that's going to suck.

It should also be mentioned that projects that try to read the filesystem into another system are always going to give you an increased risk of noshing up your partition.

So with that in mind, there is one solution that would take perhaps 30 minutes to an hour to set up that would give you near-native speed, any Linux partition support and would be just as safe (or very close to) as mounting it from Linux: Virtualise!

Yeah I'm suggesting you give up 300megs of RAM and a gig of disk space to run Ubuntu Server from within Windows. Most modern virtualisation systems like Virtualbox and VMWare allow you to pass the VM an entire disk or partition so that's what you'd do. Mount it from within virtual-ubuntu, install samba, share the ubuntu-mounted disks and mount the shares from within Windows.

It sounds like a lot of overhead but Ubuntu server is pretty slick and it won't need much in the way of resources. Once installed, you could probably get away with 150megs of RAM for it.