I was running 9 speed Sora with the same 30-39-50 front triple and a Deore RD of the same vintage as your XT, an M590 IIRC. Cassette was 12-36 and with that derailleur, it was plug and play, no roadlink necessary. Even if it is over total capacity by a tooth or two, the RD should be just fine.
For smaller granny gears, Specialite TA makes smaller rings with the correct 74 BCD for road cranks (pre 4700 Tiagra and old-school Sora). I looked into it, but replacing three road rings with Specialites TA rings was going to cost more than a new crankset.
If you're after a trekking crankset, though, Shimano trekking is going the way of the dodo. I'd get in ASAP to pick up a 26-36-48 NOS Alivio triple crankset, because it's being replaced by CUES. But also check CUES out, because there's a new adventure double that's something like 44-26, that, coupled with the right wide range cassette, should give you a really wide spread of gears. Aftermarket CUES available retail is a while off yet, though, I guess.