Would it be rude to write to an author and ask if they know how long the fic will be and if they have an end in mind?

There's this fic that I started reading when it was first posted and the author updated pretty regularly. It's awesome, but it's dragging on a bit and each chapter is pretty short. It's up to 30/? with no end in sight and I just...really don't want to keep reading this if it's a forever WiP. Would it be rude to ask? Or should I just bookmark it and check in now and then.

(This is when I wish AO3 would have a "notify when complete" notification.)