I have a suggestion! Not totally sure if this is possible, but I think it would fairly simple to add in... Why not have more voting options for polls? Instead of having just 10 options, why not have 20 - 30 or so? Just a little thing I've been thinking about. Cuz I know a couple people (me included) having to spread out a thread over several threads just to fit in 20 - 30ish voting options. Let me know if this is possible/if you like.
I had intended to go to bed before or at 10 o'clock, and it is now 22:11... so my personal opinion on the matter will come later. However, I think that regardless of whether this would be desirable or not, I don't think it will happen. It might be possible, but I think it's likely that there's some built-in cap of 10 options, that would require some hacking to change. And as far as I can tell, Aikar would rather not do unnecessary hacking of the code, to not make the option of updating to a newer version of XenForo even more distant than it already is.
I... personally do not see a need for polls with an "unlimited" number of options to be set for any particular poll. I think the cap at 10 (or whatever the "real number" is...) is more than enough for almost all uses. Especially when the options provided can be "inclusive" or specific ranges/groups of subjects, or if it falls "outside", simply put an "other, please specify" option.
I also think it wouldn't be a good idea to allow more than 10 poll options. With the maximum of 10, people are motivated to make wider categories as Joy said, which makes individual categories get more votes. Also, the poll can already take up quite a bit of space on the top of the page, requiring extra scrolling. If you want people to have more freedom picking an option, you should just have them comment on the thread or submit a form, as 10 options seems quite enough for a forum poll.