Chrome does not use OpenH264 for decoding videos at the moment (I do not know whether there are plans to change that).
I guess supporting OpenH264 in the HTML video pipeline would take some significant effort. Google usually does not put efforts into big Chromium projects that do not directly benefit Chrome (this is understandable, every business has a certain amount of resources and the business needs come first).
I am not a Googler, but I guess a community contribution of OpenH264 integration into the HTML video pipeline would be accepted. However, in order not to waste time on implementing something that will not be accepted, interested contributors should probably ask
chromium-dev
first, whether such contribution would be accepted).