Fwiw, since I have a travis-ci account for open source stuff, the fact that a draft PR wouldn’t build in the open source repo’s travis-ci account doesn’t bother me much – because as soon as I pushed my branch to github, travis-ci picked it up there. And in my case, being able to open a draft pr while travis-ci is still running for my branch would be a good thing (especially since I want to write my PR message now and then go to a different location where I wouldn’t have my PR message – and convert the PR from draft to real once I see my travis-ci account’s build has completed successfully).
I wonder how this applies to other users, are they working on open source projects, in which case, should they just try setting up travis-ci accounts? Or are they working on closed projects, in which case, I think they can ask travis-ci to build individual branches… (And yes, I’m cognizant of the “I shouldn’t be forced to sign up for a new account” attitude, I often have share it.)
Personally, having travis-ci post a note for open source repositories explaining why it didn’t build and giving users the ability to set up their own travis-ci account seems like a reasonable path forward.