This entry for Bleach
seems to signify the most important aspect of the Shonen Upgrade
Shinigami in Bleach have 3 forms to their Zanpakuto, "Unreleased", "Shikai", and "Bankai". Ichigo starts unreleased, loses his powers, skips straight to Shikai upon regaining his powers, and later gains Bankai through a pure Shonen Upgrade moment. In addition, Ichigo's Hollow powers are a similar example, powers acquired, not through training, but by dramatic need, usually after being stabbed.
bold for emphasis.
The main distinction from New Powers as the Plot Demands
would be the non-asspull nature of it. And the focus on in-universe perspective.
It's not mentioned in the description, but another feature of most Shonen Upgrades
(at least all the examples i can remember) would be it's part in character growth. It's not only a means to defeat the villain or overcome whatever threat is looming, it's about the personal growth of the character in question. The Upgrade is a part of the character's ongoing arc, often with the character's entire power set partially changing with the character's development.
I think this is something that should be included in a cleared up description of Shonen Upgrade
I do also agree with renaming Shonen Upgrade
, but not with merging.
P.S. To build on the Star Wars example, Luke's sudden reliance on The Force rather than the guidance computers to make the final shot at the Death Star in episode IV, is a fine example of suddenly achieveing mastery of a new ability in the situation which needs it most, concluding a part of character development for Luke. Said ability (and indeed his entire status as a Jedi) is showcased heavily in the next film, but is heavily outclassed by Darth Vader. This is a good (untraditional but no less correct) example of Shonen Upgrade
, while not at all being an example of New Powers as the Plot Demands