I chose 'It's complicated' because I polled for the opinion of my sweetie (British and always lived there, has two school-age children) which I'm adding to mine and my daughters' - in Ireland BUT things like this tend to get a more similar response than different one, when there's no element of Irish nationalism involved! Anyway, he thought it was a bit old-fashioned but nowhere near 'radically uncool', and couldn't see its being a problem. Daughters and I feel the same and furthermore, feel it shouldn't be changed just because of supposed uncoolth. My younger daughter says it's kind of 'retro' (which is decidedly a good thing) and older daughter says she's used Timothy for a character too.

I also chose the 'I don't think Thomas is any better than Timothy' option, but that's because I think there's nothing whatsoever wrong with Timothy, not because I dislike Thomas.

Finally, in the FWIW department, you've done the hard part already, in having such a big success with Knife - everyone who loved it will be eagerly awaiting the sequel. The small stuff, like the possible loss of a very few potential new readers (who might not appreciate the book anyway, if that easily put off!) is not worth sweating, IMO.