ActBlue is agnostic between Blue Dogs, corporatist establishment plutocrats, and progressives, its only criteria being Dem affiliation in some manner or means. It seems as if parallel channel development, especially among progressives would rock.
Besides the above linked Wikipedia background, two other links of interest: here and here.
While an easy argument can be made of no need to reinvent the wheel, all ActBlue offers is a unicycle.
Just saying.
UPDATE: Ideally a separate channel would be less replete with obnoxious and off-putting tracking links for every active link on an emailing. Some value privacy more than others; and scare tactics in emailings are a turn-off. But that is separate from ActBlue, unless they provide candidacies with emailing templates set up precisely for using tracking links, in which case they're at fault too.