Think it's safe to make this change? Is it needed with the submission of 85db1a5

It is needed because the logic for the afterRender hook is that you can change the contents after the render, this should have been sync because you want to be able to chain plugins together to have them modify things after the previous plugin is done changing it.

For example, if you have one plugin that prettifies the html and another that replaces all occurances of foo with bar, if they are done async you technically might run one before the other in an inconsistent manner or overwrite the changes that the other plugin performed.