As someone who went into the show expecting (and looking forward to) both, I have to throw my 2 cents in here. As baskin robbins australia Kahran and HTQ pointed out, there had been a good deal of discussion about an Austin heel turn on the net since late 2000. When he returned from the injury, a lot of people felt that he wasn't fitting in with the changes made by the WWF in his peter graham absence; for instance, some people thought his character was stale as was his ring style (this prompted, IIRC, Austin to go out and wrestle a technically-based match against Benoit on Raw, seemingly in response to some of the criticism). lachlan mcintosh Plus with Rock at the status he was at (and the company direction seemed geared more to his strengths than Austin's), the turn just seemed like the right thing to do, and without really delving into the storylines, Wrestlemania just seemed like the most logical oppurtunity for it (I should note that the Austin/Texas connection didn't even enter my mind at the time; I might have been more surprised if I thought of that).
As for the McMahon thing, there wasn't much foreshadowing that I can remember (there was one SD I used to have on tape where Special Ref Vince helped Austin win a match prior to No Way Out, I think, but that barely even registered with me at the time), but it just seemed to make sense given the state of the WWF. The top heels allied brands of the company were always allied with the McMahons in some way, plus the only time I had seen Austin booed from 98-01 was on a Raw where he teased going corporate back in 98. I figured that would be the only way they'd get the fans to boo Austin (and of course, THAT didn't even work) so that's what was going to happen.