Rick reported that adding online html5 validation increased testsuite runtime from 15 to 40 mins. There need to be more fine-grained control over which validations are to be run.
Also, it would be nice to find alternative to online html5 validation.
Paul sent a good e-mail summary about this and I think the decision was to just not change anything right now, but to make the validation checks optional, and just run them less often.