Messiah my dilema is the same as yours 27.5 or 29er. Leaning more towards 29er after reading all of this. Really wish test rides were easier to come by.
I understand this dilemma. I've been trying to ignore all the 650b/27.5 threads as I can bring nothing to the discussion since I haven't ridden one. My personal thinking is that over the last few years I've been loving my big 2.4" Conti Rubber Queen tyres and I miss them when running other rubber; one of the big reasons I love them is the balloon like size of them which is very nearly 650b/27.5 (Yes, I know it's not bigger than the new bigger 650b etc but its damn close to those early ones which started the whole thing). From this experience I was definetly going down the 650b route with my next bike as now that decent tyres and rims are available there are no downsides... and you can always run a 26" wheel with a big tyre if you have too (emergency) or want to lower the bottom bracket.
I've been wanting to try a good 29er for a while; but as I mentioned I didn't see the point in trying just any XC/trail bike as that is not the type of riding I enjoy. For most of last year I wanted to ride as much as I could on the bike I would be racing at the Trans-Savoie so I didn't want to change my hardtail or test a 29er and try to get to know a new bike. Now I've had the time and the opportunity to try a good 29er I have felt some benefits as I mentioned. What is a little perturbing is that just as I get to try a good 29er the industry has gone 650b/27.5 nuts and almost all AM/Enduro bikes are going that way.
But... and it's a big one; I think Chainline(Pilot)/Dipper/Nicolai are really onto something here with the Ion 15. This could be one of the first of the truly AM/Enduro optimised 29ers (See also the BMC Trailfox and Specialized Enduro 29er's). So many of the AM 29ers which have come before seem to be overly compromised by hangover XC geometry and flexy forks/wheels/tyres that they never had a chance of feeling great.
I can't get out of my head how well this Ion 15 rides, as I mentioned I just got on it and was instantly throwing it about like I had been riding it for years; I think going back to my little Helius is going to be very interesting... I love my Helius and its an awesome AM bike but I think the game has been moved forward by this Ion 15.
I'm a procrastinator but I'm struggling to come up with reasons not to place my order as soon as I can speak to Dipper.