Two* Wingnuts here; a Hyper 3 and an older Adventure (I think) of 2008 vintage. One of them has been used on practically every ride since I bought them, which has included some Alpine guiding, riding in various European mountain ranges, commuting year round and regular riding at home.
The base section of the Adventure (which is similar to a Hyper 2.5) is starting to show signs of wear and the reservoir zip is looking like it is looking forward to retirement, but when it goes I'll probably get it replaced - it's a bloody brilliant, incredibly versatile bit of kit.
I know the owner has played around with different ventures (IIRC he has spent a few years developing solar technology for the US military) which has meant supply has been incredibly stop/start, and my guess this has been reflected in the manufacturing. When Toby ran Propel and imported them he had several problems.
But TBH if I was going to replace one of my Wingnuts, it'd be with another Wingnut.
*The Adventure is a three-part pack built round a stripped-down Hyper 2, but with a 20L main add-on and a further 5L smaller pack that can be configured in a number of different ways. Complicated but amazing bit of kit.