When the first 228km section opened in March 2015, the Hokuriku Shinkansen was an extension of the Nagano Shinkansen, inaugurated on 1 October 1997 in time for the 1998 Winter Olympics, branching off the Jōetsu and Tōhoku lines at Takasaki.
The first section from Nagano to Kanazawa will be followed by an extension to Fukui and Tsuruga. Work on that section started in 2012 and should be completed by 2025.
A further extension looping back to Osaka is planned, but the route is yet to be decided. There are three possibilities, linking to the Tōkaidō Shinkansen at Maibara, Kyoto, or ShinOsaka, and they're worth a look because they provide insight into issues surrounding the routeing of shinkansen lines.
The Maibara route, with a standard shinkansen track to Maibara, is the shortest, with good access to Kyoto and Nagoya but means a longer travel time to ShinOsaka along existing Tōkaidō Shinkansen tracks that are already running at close to maximum capacity. That may become less of an issue when the Chuo Shinkansen opens as far as Osaka in 2045.
The Kyoto option would upgrade the Kosei Line to Kyoto, by regauging the line to support mini-shinkansenshinkansen or using Gauge Change Trains. With no new construction to standards that would be the cheapest option, but would limit train speeds to a maximum of 160 km/h so the trip would be slower.
The Wakasa route would involve building a shinkansen track along the shortest route to Osaka but would bypass Kyoto. With all-new construction, it would be the most expensive.
The Hokuriku line will offer four levels of service: Kagayaki (Tokyo - Kanazawa, limited stops), Hakutaka (Tokyo - Kanazawa, all stations) a shuttle between Toyama and Kanazawa (Tsurugi) and a continuation of Asama services from Tokyo on the Nagano Shinkansen line.
When the first part of the new line opened, travel time between Tokyo and Kanazawa went from 3 hours 47 minutes (taking the Joetsu Shinkansen to Echigo-Yuzawa and switching to a narrow gauge train with a maximum speed of 160km/h) to 2 hours 30 minutes.
Stations: Iiyama, Jōetsu-Myōkō; Itoigawa; Kurobe-Unazukionsen; Toyama; ShinTakaoka
Under construction: Komatsu; Kagaonsen; Awaraonsen; Fukui; Nan'etsu; Tsuruga
Route details and maps: http://www.jreast.co.jp/e/routemaps/hokurikushinkansen.html