I'm an amateur double bassist, and a fluent sight-reader. To be fair, I gravitate towards situations where reading is an asset, since it gives me a leg up on the "competition" including pro's who haven't maintained their reading chops. Plus I benefit from the networking opportunities afforded by those situations.
For me, here are the problems that I see with any new notation system:
1. "Standard" notation (SN) has created a symbiosis between composers and players. If you don't compose in SN, nobody will play your stuff. If you don't read SN, you won't be able to play anybody's stuff, and will probably not even get a chance to develop your reading skills to a performance level. The ultimate stage of learning to read is sight-reading in an ensemble with other players.
2. Learning a new notation gets exponentially harder as you get older. I started learning to read when I was about 10. It's like my spinal column has created a special circuit directly from my eyes to my hands, through my ears. A lot of time when I'm sight-reading, I'm actually thinking about other things.
3. All of the repertoire is in SN, virtually none of it is in computer readable form, and much of it is out of print. I play in a large jazz ensemble. We still maintain our entire music library, entirely on paper. For this reason, SN has much more inertia than one would expect from other "notations" such as programming languages.
For these reasons, the shortcomings of SN and benefits of new notation, are practically irrelevant. Now, "standard" notation is not carved in stone. For instance, jazz bass parts are notated differently than classical clarinet parts. I get a lot of chord symbols and am expected to play an improvised bass line.