I absorbed your comments about being too far out of the way to share the gold line up to 38th Street (in order to save costs in river and highway crossings).
I came up with an alternative which would still be able to use the Light Rail terminal along the CML. I like this route into Union Station, because it shares the same technology as in light rail technology--the streetcar can be single or double train light rail cars. This route also turns the Light Rail Terminal into a through line, opening the door for future light rail extensions northward (if that would ever be necessary).
So here is my new idea...
1.) Trains would pull out of the Union Station Light Rail terminal to the north along the CML and continue to 20th Street.
2.) At 20th Street, the train turns parallel to 20th Street and elevates over the CML.
3.) After the line crosses the River, while still elevated on the bridge, it would swing back southwestward over 19th Street and down onto Platte Street.
4.) The streetcar would run down Platte Street (either single or double track, depending on which would be best) to 15th Street.
5.) At 15th Street, the streetcar would cross under I-25 and on up to 29th Ave.
6.) The streetcar would then run down 29th Ave to Federal and that would be the end of the first phase of this streetcar line.
7.) An extension of this streetcar could go down Federal Blvd and an end-of-line transfer station at the West Corridor light rail line just south of Colfax on Federal (with a couple of stops along the way, including one right in front of Invesco Field @ Mile High).
8.) A second possible extension could be considered at the triangle intersection at 29th, Speer and Federal Blvd. It could branch off 29th onto Speer taking it into the intersection at 32nd and Federal. It could either go west on 32nd, or continue northward to 38th, then go west on 38th.
P.S. I moved this to this page in case it wasn't visible enough at the end of page 22