Ran web and mobile app locally and nothing crashes/will be doing more tests on this message spec in subsequent diffs. Also in my local stack, (with some extra code that will come in subsequent diffs) I was able to get a reaction message to "unshim" which I feel is a strong indicator that this function works as expected (see screenshots below)
Reaction Message when unsupported:
{F270042}
Reaction Message when supported:
{F270043}