I think it should be the responsibility of projects like Misskey to send out backwards compatible activities instead of everyone having to clean up their mess and be forced to implement their UI. If a reaction is basically just an image, why not send it as a reply and include a field to tell clients "Hey! If you want to support our UI here's an indicator that you can do that."? I feel like it's every other day people push for the most stupid non-optional features in existence and use the lousiest excuses for it.