I assume that the lack of inclusion is due to Prores being proprietary and thus requiring license fees to use it. Studiocoast would have to pay royalties to Apple for every sale of vmix if they included it. The best solution would be a separate purchasable plugin but beyond that the only real solution is to record vmix's output to prores with another program(such as the included software with BMD stuff or your editor's capture tool...). Frankly, other than the slightly less simple workflow I don't think there are any advantages or disadvantages one way or the other. You wouldn't gain much in system efficiency if it was integrated into vmix.