This article, by Bunita Marcus, on Morton Feldman, notation, and rubato, is well worth a look. I've gone out on a speculative limb before in these pages in placing Feldman within the Skryabiniste* tradition with regard to rubato and to its equivalent in the pitch domain, and perhaps also to timbral issues — a certain delicacy of tone without any sacrifice of drive and the use of the pedal to create an ensemble blur or an indistinct, often edgeless, but internally lively tone. (This is a perfect example of the utility of recordings: I highly recommend the recordings made of piano rolls punched to Skryabin's own performances.)
Feldman did have a legitimate connection to Skryabin, through his piano teacher Madame Press, but I'm not sure exactly what of Skryabin's music Feldman knew; he certainly did not talk about Skryabin as a model as he did about Schubert or Debussy. To some degree this is unimportant as enough of Skryabin's style is certainly as well represented as a style of performance practice as it is by the compositions themselves. Skryabinism did have a fairly wide reach, within Russia, in France through Lourie, Obouchov and Wyschnegradsky (and through the latter to Messiaen and Boulez) as well as in the US, with Dane Rudhyar and the great Nicholas Slonimsky (particularly in his Minitudes). Much of this reach was more about mysticism than musical technique (though certainly not for either Boulez or Slonimsky), but shared influences on technique can clearly be decerned — a supple rhythm, fine-grained ensemble textures, and a harmonic language that tends more towards static samplings of collections of tones than to functional harmony.
Let me briefly identify a few salient features in Skryabin's rhythmic practice. The first is a flexible subdivision of the beat, whether moving with a great sense of direction from two to three to four to five to six or more subdivisions (which connects Skryabin both back to Chopin and forward to the Henry Cowell of Fabric or the Quartets Euphometric and Romantic**), or in static ensemble textures of multiple divisions (ultimately an extension of Monteverdi's concitato style), with extended five-against-three passages, for example, as a favorite texture.
This is the first phrase from the first of Skryabin's Seven Preludes, Op. 17. In three-quarters time, against the steady eighth notes in the right hand, the left hand moves from three quarters, to four quarters in the space of three, to five in the space of three, and then to the eighth notes (i.e. 6 in the space of three), coming back in sync with the right hand. Through this written-out accelerando in the left hand, there is an increase in rhythmic dissonance that resolves as the hands return to rhythmic synchronization as well as to the d minor tonic harmony.
This accelerando is straightforward, in that the tuplets in the left hand should be played as subdivisions of the dotted half pulse uniting measure and harmonic rhythm. But other examples are not so clear, suggesting that an acellerando should be phrased as a continuous movement over several measures, rather than precisely "chunked" into complete measure-length equal-division tuplets.
Another feature is that Skryabin is often breaking phrases over bars, and not always as a metric anacrusis, leading into a phrase, but often as a sustained syncopation throughout whole phrases or sections. This play with the rigidity of the barline is clearly continued in Feldman's music, and not only at the level of the measure, but at larger scales, frequently coinciding with whole systems and pages (which Feldman usually barred prior to composition).
* I use the spelling "Skryabin" here (instead of the more common "Scriabin" or any of the alternatives) not out of any orthographic insight but exclusively out of personal aesthetics: I happen to like the shape that particular combination and sequence of letters makes together on the page; perhaps appropriate for this blog item, inasmuch as it is about notation and performance.
** I assume that Cowell's rhythmic experiments began well prior to any familiarity with Skryabin. Fabric is dated to 1920 and, although he may have become familiar via Slonimsky or Rudhyar with Skryabin in the 1920s, there is probably no certainty here until the time of Cowell's concert tour of Russia, co-billed with Richard Buhlig (later, a teacher of John Cage) and Buhlig's partner Wesley Kuhnle (who would become well known on the West Coast as a pioneering harpsichordist and authority on historical tunings and temperaments).