I'm teetering on the edge of dishing out some serious money for a Sony A7 RIII at the moment to replace my ageing Canon D60. It's not that my images aren't good, I'm pretty happy with most of them, but I do feel that I miss some due to slower focus and inadequate low light performance which are two of the things that seem to have improved massively in the last few years in all camera ranges. Just need to find the money to take the plunge.
Definitely a great camera if you have the spare cash to splurge! Personally I've found it difficult to beat the Canon 6D (Mark 1) for low light AF, even the MK2 couldn't match it! The mk2 had slightly better high ISO performance, but only marginal really. I've not used the A7 RIII specifically but I have tried other Sony's an as yet, I've always found mirrorless to lag slightly compared to DSLRs. That said the future is definitely looking very Sony at the moment!