The idea of a remote congregation isn't new. Postal missions and radio churches (breadcast sermons) have a long history, both for Unitarians and Universalists and others.
Metro DC holds testimony to the potiental power of broadcasting worship. All but two Unitarian Universalist congregations in the area are children or grandchildren of All Souls (Unitarian) and the proximate cause of the expansion was the satellite services, driven by A. Powell Davies's preaching. But the days of white-flight suburbanism and culturally reinforced worship attendance are over and we can't lean on that model reflectively.
So, I think, the first thing to consider is what kind of participation is desired of, of even possible by, the person watching or listening.
There are (at least) two complementary ways to look at broadcast worship. One, implicitly knows that the broadcast experience is second-best, but simulates the experience of in-real-life worship, with the an opportunity to participate at some important part, say by watching the elevation and fraction of the host at a televised mass, or to pray for one's own beloved dead at the Kaddish. "These experiences fill an obligation" is another way to look at it.
The other participation mode is to be a consumer of the aesthetics and information, and I'm plainly worried that as a function of our free-church mode of worship this is where the mainline of Unitarian Universalism is. It gets its value from being "the best show in town" or by being a rare conduit for some spiritual understanding. I think I can be forgiven by pointing out how unlikely the "best show" production values are, and that the more likely appeal is for those far from a Unitarian Universalist congregation. (Special spiritual understanding is possible, but let's put that to one side for the moment.) That necessarily limits the appeal of webcast worship to the already convinced, but spatially inconvenienced.
(I'd better post this or I'll never do it. But I do have some opinions of "how" based on what I've found online.)