Considering that this is solely an ALPA initiative you can expect anyone that isn't ALPA to not be considered. That being the case I'm sure ALPA would sign up anyone that was interested joining the collective instead of risking it alone out in an independent union or non-union shop. Support from anyone outside ALPA is irrelevant to make this happen.
I agree, but you need to be careful about how you set this up to make sure that it doesn't kill further organizing efforts. The UAL resolution included "seniority benchmarks" that would credit non-ALPA and non-union pilots on the national list. If this isn't done, then you'll never organize another non-ALPA group again. Non-ALPA pilots can't be concerned about losing their seniority if they join ALPA. A universal standard needs to be set that would place non-ALPA pilots in the proper place on the list if they decide to join ALPA. You can't just staple them if they join after the list is implemented.