- UX-wise, it solved many issues browsers today are still struggling with. Vivaldi is working in a similar direction, but they've basically started from scratch again so aren't close to the point of development Opera had achieved by version 12.
- These HN posts from today's frontpage [0] [1] give some idea of why we really need Presto today. Not only would it just be good to have more competitors in the space, but also, for most of its existence Presto was ahead of its competitors in every detail (except for the one important, and very political, issue of "site compatibility", a.k.a. making badly written websites work). It also, similarly, got many UX points working at an engine level that modern browsers still get wrong, like text selection of html content and link text, responsiveness of scroll and of page links during navigation, etc.
- M2 will never be surpassed by Thunderbird, and quite possibly will never be surpassed full stop (though I really hope I'm wrong about that).
... so many other things