Haha, this could be fun! Especially if it could be calculated for subsets of the to-read list, either through use of tags or if "shelves" or something similar are implemented for the TBR list.

I wonder what the best data sources would be? I know there are websites that will give you estimated reading time based on page number, and it's actually data I've started collecting for myself because I noticed that my Kobo e-reader gives me total reading time when I finish a book. If something like this were implemented here, it would be nice to have an option to enter our own estimate instead of using a calculated estimate.

I also love those kinds of numbers and calculations, and keep a spreadsheet to plan and track my reading annually. I have always used reading time estimates, though they haven't always turned out to be accurate. But it helps a little when it comes to setting realistic reading goals for the year, and especially for planning out my library holds. (Being able to place the hold based on estimated wait time and when I want to read the book, spacing out my library loans/holds so I don't end up with too many books coming in at once, etc.)

Hehe — fun idea!