OK, I know you cannot mix the two in a normal situation but bear with my thinking for a minute please:

Lately, a lot of downhillers are shaving weight/simplifying their drivetrains by removing cogs from cassettes and, in effect, creating five-, six- and seven-speed drivetrains - - still with the 8- or 9-speed cog-spacing (basically removing the inboard couple or three largest cogs and inserting spacers in their place). The reasoning is, you are lightening the cassette and eliminating extraneous gear selections.

That got me to thinking: could you REALLY lighten and clean things up by mixing a SRAM 1:1 shifter with a 2:1 Shimano rear derailleur to make a shifting setup that would move the derailleur two cog spaces for each shift - - allowing you to eliminate every other cog in a 9-speed cassette, giving you five speeds? In other words, take, say, an 11-34 cassette and use 11, 13, 15, 20 and 26 cogs all spaced two cogs apart on the cassette body. Could it work?

I can imagine downshifts might be a bit notchy; but, since most DH shifting is upshifts, that would not be an insurmountable issue. Am I way off-base here?