The best replacement for fs100 is af100.

The best alternatives to fs100 are rated as following:
★★★★★  af100
★★★★★  fs700
★★★★★  c100
★★★  blackmagic
★★★  vg900
★★  f3
★★  bmcc
★★  ea50
★  panasonic af100
★  blackmagic cinema camera
  canon c100
  fs10
  canon c300

Your alternative for fs100 is not listed? Suggest!
Speaking about fs100, one probably shouldn't forget about atomos ninja.

Other search terms related to fs100 and their ratings are:
★★★★★ atomos ninja
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fs100
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fs700