What are the pit-falls for an Open ended Sales performance?

I will start by defining what I mean by open-ended performance: This is a situation wherein there are no targets and no limit to achievements. A person or a team can go about redefining the revenues or numbers every year, and each year's sales plan starts with a zero-based process (no calculation of linear trends or progression).

When I have met some of the senior sales guys across some industries, I have heard a common thread of issues that they think are relevant to their performance and the measure of it. The most important of them all is - achievement of targets and the extent by which they surpass the number given to them (monthly/quarterly or even yearly).

Unlike technology or product, wherein the achievement for the tech guy or the product guy begins once the product is developed, a sales guy's job ends with the customer buying a product or service. Which means that a sales guy's hard work gets the deal closed, while a tech guy's or a product guy's achievement sets the ball rolling for future business. So if I am a tech/product guy, I get two shots at performance and the obvious payout - Developing + Launching a product, and getting the benefits of the product performing well.

For a sales guy who is giving his best shot and creating the kind of excellence through his work and perseverance, the performance parameters allow him only shot - that of total revenues generated, to claim that he has done great work (and probably get his due rewards).

So we have a problem here - in one hand I am asking sales guys to give their best and redefine numbers for themselves (become thought leaders in their own domain), and on the other hand I am aware that and open ended revenue target may lead to these sales guys being taken for granted.

Why will they be taken for granted?
Its like being best at all times gives others a feeling that that's your normal performance level. So if you are performing at a specific level X (quantified by the sales revenues, market share, etc) in a particular year, what will be the quantum for the next year? How much growth is really good growth in performance for you? Who decides that?

When you as a sales guy are defining and then redefining the revenues you can achieve, and then go ahead and achieve those numbers, how does a company deduce the performance parameters for you? How does an HR get that done? Is it even possible to have the best sales guys work in that kind of format?

I believe that many sales guys are not giving their best shot because organizations have designed their performance parameters (or the pathetic KRAs system) in a way that will allow these sales people to perform and excel in targets every year without giving 200% to their job. But since there is a cap on how much you can achieve, things are easy. Set 100 as the benchmark, and get 115, and then you are eligible for a reward on performance (some 15Y as a component). But how does this allow sales guys the environment to perform at their best? I am sure some of them do and then are not bothered with the kind of pittance that's dished out as rewards. But the majority are more concerned with the "extra" that they earned for the company.

Let sales guys themselves define what they think are the best ways to reward a team that redefines its own targets and works with a open-ended zero-based system.