the reasons that the "advice" i've heard upsets me is because it really seems to narrow down what exactly piano literature should be. some of the things i've heard for "strong" solo piano writing:
1) uses the entire keyboard
2) makes use of extended techniques, especially playing inside the piano
3) does not have large amounts of direct repetition (say, playing the same chord, repeatedly, in sixteenth notes, for two measures.)
4) has all those things but is basically sight-readable "because pianist don't have time to sit down and work things out."
5) no large jumps (over a tenth or so), most especially during fast passages.
Ok, so the last one was a paraphrase and me getting irritated, however, it's not far off from what exactly was said.
now then, i understand some of these things. from a technical perspective, it is incredibly difficult (and sometimes impossible) to do a wide leap incredibly quickly. however, "quickly" is pretty relative. depending on the leap, passage, etc, i can nail about a 2 octave leap and back pretty quickly and with decent accuracy, and i'm not a good pianist. yes, the passage would need more work than say a straight scalar passage, but it's not unplayable. my passage was a set of running 16th notes at 8th equal 168. so, yeah, pretty darn quick. and it was a series of repeated chords with jumps every 5th note of 2 octaves. when i brought this before a pianist at a masterclass, she said it was "completely unplayable." however, i had another pianist basically play it down, complain a little bit, then practice and nail it on a regular basis.
this gets to what is my main gripe with this idea of "how to write well for piano." It dictates styles of composition. meaning this, if i want to write something highly repetitive and bombastic, say, like "Great Balls of Fire," i would get shot down immediately. or let's say i'm doing a pointilistic piece that is entirely about wide jumps and timbre changes. make sure it's nice and slow...Or, let's say i want to write a somewhat minimalist piece that only uses the middle 2 octaves of the piano.
every piece written for piano that people love does NOT use the whole range of the keyboard. i can think of many of Chopin's etudes that, since they focus primarily on one problem, limit things such as range. also, there are highly successful pieces that use a large amount of repetitive chords (say, Hammerklavier by Beethoven?).
as for playing inside the piano...well...at this point, it's rather cliche. it's cliche because of the attitude "it's not a modern piano piece without playing inside the piano." just like on all the other instruments, it's all about extended techniques. why?
for those that have heard my music, you know i'm far from "neo-classical" or "neo-romantic." I use extended techniques, my harmonic language is usually much closer to atonal than Tonal. in fact, i'm never Tonal, but i do work in free triadic harmonies on occasion. and yet i'm insulted when someone tells me "piano music is only good if you use the whole keyboard, play inside the piano, don't have banging repetition, and avoid large leaps." great, i'll just go write against Listz. and fail.
the best part was in the masterclass when the pianist asked me "did you even play this at a piano?" and i responded "Yeah. i've played for about 19 years, taken lessons for about 12 of those years. I can hack my way through the piece pretty well. and i am most definitely not a great pianist." After that, the session ended. I more or less pointed out that this pianist was a TERRIBLE sight-reader. i mean, really really bad sight reader (messed up a couple easy pieces people brought in). i don't care if you have multiple CDs, if you can't sight read, to offer to read pieces. when i did a masterclass on writing for trombone, i said "please send me files ahead of time for me to look at. don't expect me to sight read them day of, cause they won't sound very good."
ok, end rant. At the end of the day, if you have an artistic vision for a piece, and it isn't completely impossible (some things are, like, say, a 18 note chord played without the aid of a special device.) then go with it, and don't worry about what some people say. there are millions of pianists in this world, more than likely someone will like your piece and be willing to play it. if not, you may find someone professional enough to play it anyway.