It's not a bad idea, and a definite upgrade in terms of evaluation, but in the end it's still a very small sample size. I always have my 25 man roster set before ST begins, and no matter how hot a guy gets for 50AB's will that change. Of course, that's my personal preference, and don't expect everyone to hold that point of view.
Travis' idea is great and has been discussed before in relation to an Arizona fall league and I would personally LOVE to see something of this sort. In realistic terms, I don't see this happening soon, so I would happily settle for a 3 day ST.
And remember, WiS, a season which is shorter by 3 days, means a 3%+ increase in profits!!! Everyone wins!