With the introduction of YAML, there's an opportunity to discontinue the separation of FalloffReaction and ChemicallyActivatedReaction prior to release to production. The classes differ in a single detail, i.e.

Rather than specifying a chemically activated reaction as a separate type:

- equation: ch3 + oh (+M) <=> ch2o + h2 (+M)  # Reaction 1
  type: chemically-activated
  low-P-rate-constant: {A: 282320.078, b: 1.46878, Ea: -3270.56495}
  high-P-rate-constant: {A: 5.88e-14, b: 6.721, Ea: -3022.227}
  Troe: {A: 1.671, T3: 434.782, T1: 2934.21, T2: 3919.0}

the following equivalent would be sufficient:

- equation: ch3 + oh (+M) <=> ch2o + h2 (+M)  # Reaction 1
  type: falloff
  chemically-activated: true
  low-P-rate-constant: {A: 282320.078, b: 1.46878, Ea: -3270.56495}
  high-P-rate-constant: {A: 5.88e-14, b: 6.721, Ea: -3022.227}
  Troe: {A: 1.671, T3: 434.782, T1: 2934.21, T2: 3919.0}

i.e. over-riding chemically-activated being false by default for falloff reactions.

It's also relatively straight-forward to deprecate the remaining instantiation calls (i.e. XML and from scratch). Changes in the converters (cti2yaml/ctml2yaml) are likely trivial.