I'll tell you what I don't want. HBARs, or M4 profile. Don't get this obsession with M4 cuts, they're useless. I believe that Noveske is doing it right with his new N4 barrels.
Things that I do want;
They should be government profile or a medium contour under the handguards,
Taper pinned FSB should always be an option,
1/7 twist, M4 feedramps, metal should meet MIL-B 1159, chrome lined.
I personally prefer 11.5" over the 10.5's, but 14.5" without M4 cuts are nice as well.
Stainless are nice as well, easier to customize because they don't need refinishing, no chrome to chip or peel. I would prefer something tougher than 416, like 410, beadblasting is a nice option, and FSB should still be an option.
Chambers should be 5.56mm or perhaps .223 Wylde would better suit the majority.
ETA: Don't forget about middies. I'd love to see a good midlength that duplicates the GI dimensions forward of the FSB. In other words, you could mount a bayonet and it will sit in the proper location. All the current 16" midlengths are about a 1/4" too short to allow proper bayonet mounting. Again, government profile or a medium (.750?) contour. Anyway that's my .02 cents worth, do with it what you will.