Lately I've been playing a lot of Chopin's work from the 1840s, and, aside from lesser works like the Tarantelle, I've come to enjoy a good many of them more than his earlier work. Perhaps there is less ardor, less youthful passion, but his compositions from the period seemed to be building up, crystallizing, becoming more contrapuntal. I can't help but wish he had lived to pen another set of Preludes (perhaps Preludes and Fugues) or Etudes, informed by his greater life and intellectual experience.
On the other hand there is Scriabin. His late music, to me, is among the most intense of all music. He died at the cusp of a great transformation of his country, a transformation that turned out disappointing, even lethal for some creative artists. In his sketches for the Mysterium are many "12-tone" sonorities--large chords with all tones of the chromatic scale, but with different distributions (which make them harmonically quite different). It seems to me like he had little room to tread, as he was exhausting the harmonic possibilities of our tuning system, that his creative mind would be forced into greater examination of form and timbre. While he did express fascination with other tunings, and some scholars believed he might've chosen to compose microtonally, given the time--unless his presence would've altered the politico-artistic environment of Russia in the 1920s, he would only have a good ten to twelve years of composing before censure became so intense and dangerous that he would likely have had to double back on his ideals or keep his work private.
I'd be interested to see other people's opinions--which composers seemed to be just on the cusp of something, and which ones, even if they had untimely deaths, seemed to reach a maximum of expression which would be both difficult to sustain and to further develop?