Even though BotCon didn't become "official" until 2003, they were supported and endorsed by Hasbro from the beginning in 1994, producing exclusives and presenting panels & displays each year (except in 2004, as there was a (paid) licensed convention at the time, and Hasbro couldn't be seen to be involved in that year's BotCon).
The BotCon name is still iconic, and if Hasbro had the sense to see the value of a proper fan-run convention by working with the new BotCon people, it would draw in a lot of people (Hasbro interaction and reveals are the bigger drawcard), there is still value in the BotCon name... as a Convention, not as a brand for hocking merchandise as the new owner is doing. As one of the biggest fans of BotCon, I have no interest in buying "BotCon" merchandise that isn't "Transformers" merchandise (because they don't have licensing to do that), and doesn't have anything to do with an actual convention event, as I buy the BotCon branded items (like t-shirts) because it is a keepsake of living the event.
I know that they have had some novelty items that have proven popular over the years, but usually they have something Transformers related on the item as well.
If an Australian fan wanted to go to a Transformers convention in the next year or so, the biggest one that is exclusively Transformers would be the TFCon that they have on the West Coast or Los Angeles, as it will have the most Transformers guests (the drawback for purists though is that TFCon is mostly funded by 3rd party producers, so it is very much a "3rd party convention with Transformers guests"). Otherwise, for a convention that isn't exclusively Transformers, the SDCC is indeed one that is very popular... which can make it very difficult to get into, and expensive.