Latest i heard from from the polling guys is that Tsai is leading slightly in internal polling. That said, the polling people have some problems with their methodology..so its really hard to guess who will come out ahead. That said, it is quite true that a big factor in the results will be the turnout. In 2010, because of the rain etc it was predicted that the blues will not come out..and then someone got shot. (So everyone blamed that for the narrow loss)
That said, the DPP factions have somewhat united behind Tsai and it showed in the campaign thus far...so turn-out on polling day should be good if everything goes to plan. That said, a lot of things can happen from now till polling day but I think for the past few years it has been that there's always a 'surge' at the end for someone. Which is good for Tsai..
Disclaimer : I'm somewhat DPP so I'm biased..
There should be a poll to find out if people answered truthfully in polls.
After that, another poll to find out how many people answered the above