Don't think that is exactly practical for many flights... Specially around Eastern Europe...
And there flights weren't even officially targeted. This flight was intercepted by an armed military jet. From there it can quickly escalate in the event of a misunderstanding.
Qatar was doing massive detours a couple of years ago to keep flying (of course money wasn't an issue for them)
But detouring Bielorussia might be even cheaper than forced landings, who knows.
Unless Ryanair's reputation takes a big hit, I'm guessing the answer is all of them.