I am in the same boat, Surface is exactly what I want and does everything I want it to do but, it is, as you say, a flawed product, of which Microsoft was fully aware and of which they have completely washed their hands once its three years old.
They will only sell you a replacement at an exorbitant price when these flaws surface (pun intended) and add insult to injury by offering you only a quarter of that amount as a part exchange if you want to replace with a newer model.
I would only consider a new surface, or for that matter, another Microsoft product if they were to offer a fair trade in value on the defective Pro 4.
My question is how can we initiate a dialogue with someone in Microsoft who has the ability to make these decisions? At the moment we are stuck in support hell where the CSR's can only sing from the hymn sheet they have been given. Its not their fault, they are only doing their jobs. We and Microsoft both know there is a problem and it seems to me Microsoft must step up to the plate and do something about it.