Starting anything from scratch is a huge risk these days. At best you'll have something like the python 2 -> 3 rewrite overhaul (leaving scraps of legacy code all over the place), at worst you'll have something like gnome/kde (where the community schisms rather than adopting a new standard). I would say that most of the time, there are only two ways to get a new standard to reach mass adoption.
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Retrofit everything. Extend old APIs where possible. Build your new layer on top of https, or javascript, or ascii, or something else that already has widespread adoption. Make a clear upgrade path for old users, but maintain compatibility for as long as possible.
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Buy 99% of the market and declare yourself king (cough cough chromium).