With still a few days, possibly weeks to go until the detailed results, I might as well analyze the data we have so far.
Generally speaking, compared to last year Youmu has widened the gap between her and the characters below her as well as closed the gap between her and the characters above her. Not only did she manage to pass by Koishi, she's also gotten really close to Marisa.
Total participation has gone down a lot since last year: It's hasn't been that low since 2009. Because of that Youmu also has lost more than 1100 points compared to last year, however other characters in the Top 5 have lost much more.
Youmu's first choice votes have only diminished by about 150, whereas it has gone down by several hundreds for Koishi and Marisa. So, her first choice rate has actually risen to 31%. Despite the increase, Youmu's rate only ranks at 4th place with Wriggle being the only one with a higher rate within the Top 100.
In absolute numbers it's again the second highest number of first choice votes and has gotten even closer to Reimu's.
I personally think that the numbers reflect an increasing disinterest in the Touhou Popularity Poll, whereas fans passionate about specific characters remain interested. The main reason for this development is most likely the lack of new characters since last time.
Honestly, if Youmu somehow managed to replenish her popularity among the general Touhou fandom, she would have a really good chance to reach first place. A single (non-cameo) appearance might be enough.