Note: I’ll be updating these INT section descriptions with much more detail in the coming months.
INT route winding up the Wind River drainage in the Gospel Hump Wilderness
A very rough mileage estimate for the Inland Northwest Trail (INT) based on GIS data used to create the draft route map puts the trail length at between 1,400 and 1,500 miles long. Much of the proposed INT route is on existing U.S. Forest Service trails; other public trails; and like many other long-distance trails, the route also includes some forest and rural roads to link up the more wild and scenic portions. In the future, new sections of trail could be built to replace some sections of the INT route that are currently on roads. Other sections of the 2012 proposed route could be re-routed in the future for other reasons. There are many small towns near and along the route where hikers can resupply and take a day or two off the trail to relax or find other adventures such as mountain biking, paddling, rock climbing, fishing, wildlife watching or visiting historic sites.
The INT passes through some diverse landscapes I’ve broken up into the following 13 regions or sections (which I’ll be adding much more detail to soon). While the trail could be hiked either direction out of Spokane and the route description here is clockwise (east), the most desirable direction to thru-hike the INT would likely have you headed out of Spokane headed southwest on the Fish Lake and Columbia Plateau Trails towards the Blue Mountains of NE Oregon. Have thoughts or suggestions on the route? Just e-mail Derrick at inwtrail@gmail.com.
Section 1: Spokane and North Idaho Centennial Trails (Spokane to Coeur d’ Alene, ID). Mostly paved trail along the Spokane River.
More info: http://www.spokanecentennialtrail.org/http://www.northidahocentennialtrail.org/
Section 2: Coeur d’ Alene Lake to Pend Oreille Lake (Coeur d’ Alene to Sandpoint, ID). Mostly dirt trail but some road and paved trail walking.
Section 3: Selkirk Mountains & ID/WA Stateline (Sandpoint to Metaline Falls, WA) Mix of trail and open and closed forest roads .
Section 4: Pacific Northwest Trail (Metaline Falls to Montana) This section of the INT follows the Pacific Northwest Trail route on beautiful and rugged trail and some country and forest roads east of the Selkirks.
Section 5: Purcell Range and Cabinet Mountains (PNT to Troy, MT, then Trout Creek, MT) Mostly trail with some forest roads. Some very rugged cross-country, off-trail sections likely through the Cabinet Mountains Wilderness.
Section 6: Bitterroot Mountains (Trout Creek to Avery, ID; Avery to ID/MT Stateline; St. Joe Lake to Highway 12) Mix of trail and forest roads, with an incredibly scenic paved road hike up the St. Joe River, and a long traverse of the Bitterroot Divide on the Idaho/Montana Stateline.
Section 7: Selway Bitterroot Wilderness (Lochsa Lodge, ID to Paradise Guard Station) Highly remote and scenic wilderness trails.
Section 8: Frank Church Wilderness to the Salmon River (Paradise Guard Station to Riggins, ID) Wilderness trails through the largest wilderness area in the lower-48 states with a few road crossing along the way, finished with a world-class, beautiful mostly dirt road hike down the Salmon River to Riggins.
Section 9: Seven Devils and Hells Canyon (Riggins to Joseph Canyon) Nearly all trail hiking with a couple road crossings and a jet boat shuttle (or short swim) across the Snake River in the deepest gorge in North America.
Section 10: Joseph Canyon and the Grande Ronde River (Hells Canyon to Troy, OR) A mix of forest roads, closed roads, and historic trails through infrequently visited canyons and high plateaus from the rim of Hells Canyon to the Grande Ronde River.
Section 11: Wenaha-Tucannon Wilderness & the Blue Mountains (Troy, OR to Walla Walla, WA) Mostly wilderness trails with a final road stretch into Walla Walla.
Section 12: Columbia Plateau Trail (Walla-Walla to Cheney, WA) Country road walking from Walla Walla to Pasco, then crushed rock surface rail trail through the Columbia Basin to Cheney.
Section 13: Fish Lake Trail (Cheney, WA to Spokane, WA) This final leg back into Spokane mostly on a paved rail trail, with a few miles of road walking to mix it up.
Friends of the Inland Northwest Trail 
Looks like a really great trail. I know many of the different areas from when I used to hike and climb in the Inland Northwest more than 25 years ago. Good luck with the project.