Currently the NMC membership is tiny. Likely the linalg focus is due to the biases of that group. Getting an open-source project involved in something like this isn't so terrible, if the vendors allow it (i.e., if it isn't a sham for one set of vendors to gang up on another, as the Open Software Foundation was about 15 years ago). I notice that Research Systems (IDL) conspicuously isn't on their list (they'd definitely be more array-oriented). Also conspicuous by their absences are prominent groups like NAG and netlib.

As for coming up with the fee, I think that it wouldn't be a huge investment for STScI and Enthought to split. If successful, NMC will impact both organizations quite a bit, so it should be worth it to them. Of course, I don't work for either organization so that's easy for me to say. Note that these people expect their members to do a lot of work, so the greater commitment might be time. However, the group is conveniently located in Austin...

Alternatively, we could petition for a waiver based on our lack of profit. That's been done successfully in the past, too, for example by the Gutenprint folks (who then proceeded to teach the developers at Lexmark et al. a thing or two about dithering). XFree86.org had to beat on the X Consortium (or whatever they were called then) a bit, but eventually got in. I'm not sure what the deal was with fees for them.

--jh--