1. It's too expensive for what it does.
2. It's too big for what it does.
3. What it does it pretty sweet, though.
4. There is no Number 4.
5. The only people who are going to buy this are the Strymon True Believers who already have a BigSky on their board, so they don't need to make additional room for it. They will also buy the TimeLine MX and Mobius MX, even though those will also be too expensive, too big, and sound great.
I will say one very good thing about the BigSky MX. It brings a long duration IR/convolution engine into the the mainstream of the effects world, and because Strymon has chosen to do this, they have pretty much ensured that all their competitors will follow suit in their next generation of products.
Currently, the only long duration IR pedals I'm aware of are the Logidy EPSi (defunct), the Poly Effects Verbs, and the Tasty Chips Integral. All other IR pedals on the market only accept short duration IRs (200 ms or 500 ms).
Meris, Boss, Line 6, Fractal, and Source Audio have just been put "on notice". I'll buy the Boss GT-2000Core, when it comes out. It will be better, smaller, and cheaper than the Strymon BigSky MX, just like the Boss 500 series pedals are better, smaller and cheaper than the first gen Strymon pedals.