Interesting debate folks.
I love evaporated milk (I take it that we are talking about 'Carnation' here) and grew up with it as an addition to puddings/desserts.
As others have said, I think, if included in the base, it could limit the versatility of the base to be used over many dishes. For this reason, I don't use coconut in my base either. In my opinion, a base sauce/gravy should be a pretty bland affair - adding texture and volume to a curry sauce, and the essential background flavours, without being overly noticeable in the finished dish. Too much sweetness in the base, I feel, limits the ability to produce an array of curries from the same base.
I think evaporated milk could have it's place in creamy (korma/CTM) type dishes - might give it a try.
I'm also curious as to whether it would work in H4ppy Naans. Many will know that I am a great advocate of the H4C naan, but admit that the original recipe is too sweet (for me), so I reduce the sugar. But as it uses milk and not yogurt, the sweetness of a proportion of evaporated milk might work.