Valve has been working on a physics engine called Rubikon since at least 2012. [1] Maybe it will be used to fully replace Havok in Source 2.
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[1] https://www.youtube.com/watch?v=YTC0V0LWeGI
[1] http://media.steampowered.com/apps/valve/2014/Sergiy_Migdals...
[1] http://media.steampowered.com/apps/valve/2015/Migdalskiy_Ser...