After waiting for an mtDNA haplotype match to come up on YFull for years I finally found one yesterday. And the guy is just up the road (relatively speaking) in the Gold Coast, Queensland and wrote back the next day, which is amazing.
However, there are a number of issues that will make this match less than useful in extending my tree:
1. His name is John Brown, which isn't very distinctive.
2. His maternal family entered Australia via Tasmania, while mine is associated with the Ballarat Goldfields.
3. We don't have an auDNA match on GEDmatch, which tells me this link goes back many generations.
4. There are multiple non-paternity events in his immediate upline, with DNA confirming that his mother and her sisters had different fathers and his aunt was first cousin to his father-in-law or something. Not that this is relevant to mtDNA but it seems to confuse him, because I couldn't understand why he was mentioning it in relation to his female line.
Oh well, it was worth a try anyhow. As if tracing Irish genealogy wasn't hard enough ...