The measure is miner consensus. How do you intend to measure exchange/merchant acceptance?

Asking them.

In fact, we already have. I have been talking to well known people and CEOs in the Bitcoin community for some time now. All of them support bigger blocks, this includes:

Every wallet developer I have asked (other than Bitcoin Core)
So far, every payment processor and every exchange company

I know Gavin has also been talking to people about this.

There's a feeling on this list that there's no consensus, or that Gavin and myself are on the wrong side of it. I'd put it differently - there's very strong consensus out in the wider community and this list is something of an aberration.