I can see the problem it is for a TO. I guess one way to handle it is before the tournament starts is to lay out the specific guidelines you will be following concerning time limits and such, and decide before hand whether the final will be timed or not. Sometimes reminding everyone at the beginning about stalling and that you will be watching will eliminate the potential problem.
I'd just like to bring up the fact that this was a Grand Final match. There was no time limit and he was behind in points. He had no motivation to stall 'for time.' Meanwhile he did have reason to be very critical and deliberate in his movement... Which is another reason for my hesitation in disqualification, and was under the impression prior to the first warning that 'there is no stalling in a game without a time limit.' (Paraphrasing) It seemed more likely that he was suffering severe analysis paralysis or was trying to frustrate his opponent, but it was very difficult to discern which.
However, intentional or not, his slow play was detracting from the experience and performance of his opponent.
I understand that disqualification is the job of the TO, but in a situation where motivations are uncertain I find it a difficult call to hand out, especially in Grand Finals.
I'm not asking for a hard time limit either, FFG should even stress that it's the job of the TO to determine what the situation is at the table and account for it when making any decision to disqualify tournament participants. However, some indication of where to consider drawing the line would be nice. For the slower players among us, 5 or even 10 minutes may seem totally reasonable. This is why it helps to have a guideline even if not a hard limit.
I also think that Grand Finals matches should be timed. Perhaps given an extra 30-45 minutes over normal rounds, but a time limit encourages aggressive, exciting play, makes player motivations clear for the sake of calls like this and adds urgency to the players' timing. Also it would let a poor T.O. get home before midnight.