9 speed shimano allows you to easily use their mtb kit to find triples and long cage RD.
This is definitely interesting, I've got a 9-speed LX RD kicking around and a 9-speed cassette, so I'm thinking that some Tiagra 2x9 brifters and a suitable rear wheel would allow me to at least try it out.
10 speed road and MTB don't play nice.
Stick to Sora unless you wanna hunt around for the pull ratios and try to get something 10 speed.
IIRC Tiagra 4603 works with 9 speed XT to allow for 11-36.