Went to the NEC show today, almost entirely to see this monster, and either rule it in or out. I'd hoped Wednesday would be a quiet-ish day and indeed I was able to spend a considerable time inside the 600, poking, prodding and opening things, and talking at length to the enthusiastic and surprisingly knowledgeable VW staff.
Some of the questions I wanted answers to were
1) Is there enough room to fit a bike (or 2) leaned over under the bed when it was in use?
Answer - No. However it would not be a problem fitting 2 bikes in the "corridor" even when both beds in use, but you wouldn't want to travel like that so a bike rack would still be necessary - a big negative for me as it was one of the reasons for moving to a bigger van.
2) Could I fit in the upper child's bed if I wanted to use the van for a solo trip and keep the bike/kayak and other stuff in the back with the bed folded up?
Answer - Yes! This really did surprise me. I had to lie diagonally, and it's a bit clautrophobic with the roof so close, but it would be workable - a big positive for me and goes some way to balancing the previous drawback
3) The biggie - Could I really live with those looks?
Answer - Yes. Yes I could. I'm not pretending it's as handsome as a T6, but I found it a lot better looking in the flesh than in photos and I could live with its lack of looks for the interior, which pretty much answers everything I want from a campervan. I don't care if other people don't like it, I don't buy things to please other people.
Other observations were that the fit and finish inside is better than any campervan I've seen, just amazing and the sort of automotive quality interior that can only come about by mass manufacture of shaped-to-fit panels. It really did feel (almost) worthy of its price. I looked at a couple of other manufacturers take on the Crafter and they just weren't even in the same universe. The cab seats felt bigger, more comfortable and more supportive than the T6 ones. The only niggle I could find with the interior was the aircraft style lockers. Unfortunately, although they look a decent size, all the volume is in the lid. Once you open them, the actual floor area inside is only a few inches deep. You could put soft things in the lid and then close to squash them in, but they have gone for form over function there and they could have made them a lot more useful with a different design. It's not something that would put me off though, after a poptop T6 I'd still end up with as much storage as I'd ever need. The dashboard is a bit utilitarian and is the only bit that still looks cheap and dated due to the low quality plastic used. No comfort dash option here.
Oh one more. I've bemoaned a couple of times that the Crafter redesign was a bit of a copout and kept the same dimensions, meaning that unlike a Sevel, it's not wide enough to sleep transversely. They've tackled this on the GC600 by having indented panels which stick out a few inches on either side and I tried the bed (which was wonderfully comfortable) for size. I could fit, but only just! With my head as far up where the top of the pillow would be, I found I could just touch the opposite end with my feet. Now I'm 5'8", if you're 6 foot plus you would need to sleep a bit diagonally to be comfortable, which is fine if only one of you is that size, but if your partner is also a six footer I'd have a damn good trial in one before handing over my £70k+. It may not even be a problem for everyone either, an ex of mine was nearly six foot, but she always slept with her knees up, whereas I seem to sleep with my toes pointed like a ballet dancer (though without the physique

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I didn't go in the 680 as it had a lot more people crawling over it and it wouldn't be a model I'd be interested in anyway.
The T6 Cali was represented on the VW stand by a nice Bamboo Green example, though a bit surprised it wasn't a 6.1.
So a major decision for me now. My options are to keep the T6 and embark on a serious of improvements (justified by the money not being used to get a new van now being available for spending right?

), the Grand Cali, or the only other van in the running, the Westfalia Amundsen 540 (Ducato) which beats the GC in every practical category, is £15k cheaper and would undoubtedly be what I'd go for if the GC didn't exist. The cost to change to the GC600 for me would be circa £30k so it involves a considerable sacrifice and will take a lot of thinking.
If you've read all this waffle, sorry, but putting all my thoughts down is helping that process.
Be interested to hear if anyone else isn't repulsed by its looks and is also considering one.