The original preliminary design, environmental, and permit work for Phase 1 (Vegas-Victorville) was for electric, aligned for speeds of 150-180mph generally following (often within the r/w of) I-15. The NEPA documents are still available at the FRA web site. I've noted before that the age of the documents suggests the need for a little update work, and that if Virgin/Brightline wants to start with slower diesels and/or a modified alignment (they haven't said, really) that will almost certainly be the case.

Xpresswest milestones list: [www.xpresswest.com]
FRA NEPA documents (from 2011): [www.fra.dot.gov]

FRA has a moderately well-hidden web site for all of its NEPA documents and related information going back a decade or more. Interesting place to browse occasionally. See: [www.fra.dot.gov]

High Desert Corridor (Phase 2 of the HSR project, Victorville-Palmdale connecting with Metrolink) info is mostly at LA Metro's web site (https://www.metro.net/projects/high-desert-corridor/) including the draft and final EIR/EIS documents. More info is a San Bernardino County's web site (http://cms.sbcounty.gov/dpw/Transportation/HighDesertCorridor.aspx).

The Vegas-Victorville environmental work was for obtaining permits and building it - a true project-level document - unlike most of what has been done for CAHSR outside of the Valley section that's under construction. The HDC work is a little more programmatic as far as rail is concerned (it's really for a freeway), but covers the basics and should be relatively easy to tier from for the rail line.

With Branson's name recognition and Virgin's reputation for hard-nosed analysis and project implementation (not only Brightline, but other train, airline, etc. operations) this seems to be the best chance to get the money together and build it yet. Note that back around 2012, the project did qualify for a FRA loan, which was pulled at the last minute when a newly Republican Congress ordered them to do that; the decision to kill the loan was completely political, not economic.