The styles of custom builds may be changing, but I would say the world of mad custom Minis is still alive and kicking. It is however slowly migrating away from the main Mini scene and towards the general modified car scene due to the Mini scene becoming less accepting of these sorts of build as the cars get older. The general modified car scene is a much more welcoming place when it comes to more radical builds incorporating styles and trends from other car cultures like hot rods, stance, race cars, etc. These builds also tend to be created by younger people who focus more on social media rather than online forums (I try to do both!).
Of course everything I've said above is just my observation as someone who is headily involved in the Mini scene and custom/modified car scene at the same time. That being said, I was at London 2 Brighton over the weekend with my car, and I received many lovely comments during the day, despite some of the things I've seen said about it online 
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These sort of builds look great and really stand out from the crowd of BRG cooper replicas (which also look beautiful) but I kind of think of car shows like visiting a car museum... would you visit a museum with all pretty much identical cars in different colours or would you prefer different concepts and people's imagination gone wild on the same canvas
I think whoever said about the days of £200 minis has a good point... as some of what I remember seeing at shows growing up was essentially a rotten shell put onto a random chassis.. or like the early 2000s show Chop Shop where it was just filler formed in to any old shape over some hacked and tacked bit of bodywork.
But even IMM in 2019 I saw the orange air ride mini bouncing about.. one with a Harley engine out the front.. 6 wheeled pick n mix van and I'm sure a few more weird builds.. but it seems every year/event is less