Why engage with a company that have proven themselves to be an enemy of Free Software? I'm not buying their "how do you do, fellow Linux users" facade.
SDL is a project with a long history, so let's pretend they move a backlog of 5,000 issues over to Github. Everything is great--now users can search, discuss, open, manage, etc. all these issues on a slick web UI. People are happy and things just work.
Now some years later there's a blog post from Github, "An update to our free tier" that outlines dramatic changes. It turns out Microsoft needs to make some changes to keep their shareholders happy with their returns. Now Github only allows 2,500 issues per repo on the free tier--you'll be wowed with slick graphs that show for 99.999% of users they'll never even know or notice this new limitation. People will post long comments on the Hackernews thread about how 2,500 issues ought to be enough for anybody and that Github/Microsoft actually love developers _more_ because they're willing to reduce the features than shut down the business.
And now SDL is in a bind.. a free project that generates no revenue now is facing a dilemma. Should they pony up real dollars to keep the history of their 25+ year old project? The cost of moving source control isn't trivial and is a huge ops burden that keeps the devs from doing real work... and cha-ching out comes the credit card, out goes a $100/mo then $200/mo etc, etc. charge.
This isn't some wild speculation, look at Microsoft products like Onedrive that clawed back huge free tiers of storage in the past. It's just an inevitability with commercial software that costs will rise and someone will be squeezed for money.
So the threat is some number of years down the line they may have to go back to paying to host and maintain the infrastructure themselves again? I'd take that deal.
It genuinely surprises the shit out of me that people haven't created a "middleware" layer that treats GitHub as its backend / source of truth, but everything gets routed through a custom domain. E.g., spin up this glorified reverse proxy on Heroku, and now example.com/bugs is really just example.github.io/bugs, which is a page with all its form actions pointing to the Heroku service acting as a go-between for managing github.com/example/whatever/issues with full backups, etc.
It's probable that in that instance they could just pay for GitHub datacenter or whatever Microsoft chooses to name the new evil plan. But Microsoft has little reason to turn evil again (open-source projects generally have little money and won't spend it on source control/issues when there's a free competitor), as we're at a crossroads where nobody needs Microsoft software anymore (iOS/Android/Mac/Chrome OS for personal computing, Google/Amazon for cloud), so they need the advertising for their cloud. Therefore, $500K per year or thereabouts to host all of the open-source code on GitHub and provide some amount of CI minutes is worth it to get people to ask for GitHub/Azure at work.
Look, I don't know. Speculating seems like a pointless exercise, and I'm already being downvoted for not liking Microsoft enough. I think I'm just about done with this website.