As we approach LC2 and beyond, it becomes important to slow down the rate of feature additions, so that the spec can be stabilized. Post-HTML5 versions should be the staging ground for new features. Therefore,  we should allow counter-proposals to use "too late to add features" as a technical argument against a proposal that suggests adding features. This is not necessarily dispositive in itself, but would weigh against the relative harm of adding a requested feature in a future version.